1988 - 2002 OBS GM Truck Tail Lamp (Brake Light) Circuit Board Diagnosis & Replacement (Chevy & GMC)

[@hawkhootch]

Great video, thank you! Fixed my 1997 Z71 for 18 bucks. I appreciate the help!

[@eddiebashaw8427]

Thank you so much for this. I had no idea there was a Circuit Board. I replaced the lights and still nothing. Now that i have replaced the circuit board its all good. I have a 1998 Chevy Silverado. I guess 23 years isn't bad.

[@manuelsaldate.3920]

No hablo Inglés, pero me sirvió a la perfección tu Video. Lo mismo le pasa a Mi Suburban 1998. Una ocasión los desarmé para limpiarlos por dentro, y me dí cuenta que están algo quemado donde van los focos, igual que el tuyo. No presentaban falla permanente, pero ahora sí. Voy a buscarlos para cambiarlos. Muchas gracias! Saludos desde Tijuana, México.

[@mmm_L.817]

Just wanted to say thank you for this video! I had no idea there was a circuit board in the tail lights and this almost solved our problem entirely. Unfortunately, we also have something going on where our tailgate is effecting the tail lights functioning. However, without this video I doubt we would have ever gotten as far as we did on this repair... So, thanks again!

[@dalehammond1704]

Thanks much! You saved me a lot of money and more importantly, time. I replaced the bulbs in the taillight of my Silverado and it still didn't work. When I saw your video I picked up a new circuit board and now it works perfectly. Now I have a brake light, turning signal, etc.. My circuit board looked perfect (no burn marks) but it was still defective.

[@jonslagle6501]

Thank you so much for this video helped get my turn signal working again on the 99 suburban 18 dollars later but better than taking to a shop!

[@noaolvera1750]

Spent like 15 dollars on bulbs it was the circuit the whole time thanks man good video

[@rogerwilliams7541]

Just noticed and viewed this video...like the diagnostic technique and explanation...spot on and most informative! thanks!

[@ric.huerta01]

Thanks for that informative video man.. and all this time I thought it was a bigger problem! 🤦🏽‍♂️.. all these years and now I figured it out thanks to YOU!!! 👌🏽💪🏽👊🏽

[@AmericanPatriot1778]

Have an 89 K1500, circuit board lifts up a little to where there is no contact between the white board and black board, traces to the plug lift to where there is no contact. What I did was place a 1/2 self tapping screw from the inside out close to the break light to keep the boards together. I not had any trouble with the break lights in over five years. Did the same on a 94 K1500...

[@MyWorldMyWay81]

I just inherited a ‘98 Silverado 1500. This is my first project on it. Thanks for the education. Much Respect

[@hadbl12]

Very informative... I think I have that same problem, but on the right side. I will try what you showed on this weekend

[@rubenrendon9225]

Great video! I have to change mine cause the last owner super glued the bulbs in

[@cutlasscrazy6081]

I have the same screwdriver and the same meter. And the same problem. Great video. Thanks for the very easy help. Including part numbers was a huge bonus.

[@robertnovotny4588]

Thanks for the video step by step and explained in detail.

[@marvinjackson7328]

Thank you for the video cause my lights is out in a bag and in I had that same trouble before

[@mb391]

Thanks! This was just what I needed.

[@daniellara306]

Thank you for this video! Tons of help!

[@rolandosanchez3664]

Great video thanks but me I first check the bulb to see if it looks black then I look closer and check the filaments I even tap on the bulb because they can look good but it’s not it has a break on the filament.

[@1234krise]

Exactly what my truck needed!

[@sdushdiu]

Excellent and very useful video! Thanks!!!

[@laudennn]

ah yes the circuit board repair -- where i take it out throw it away and put in a new one. nice repair video

[@DrShock]

Thanks. Yeah, thermoplastic traces are not serviceable.

[@dustandshadows3179]

For this problem all you have to do is bend the wire out at the center of the new light bulb so it makes contact. The new bulbs are thinner at the connection than the old original bulbs thus they don't make good contact

[@DrShock]

That's certainy something you can try, but that's not the situation being shown in this video. The boards circuit tracings crack with age and over road vibrations, as well the unplated metal corrodes internally. I show this in the video by moving the bulbs between boards to eliminate the bulbs themselves as the problem in this scenario.

[@IqarP15]

Had this problem today on RH and it was very hard to get the bulbs out because the sides looked like they were glued in being a 95. So I will find a place that has this assembly for a Silverado.

[@Nomadcreations]

Good vid. & Isaiah The Brake Lights Cancel out the 4 Ways Circuit

[@harrymuhammad9835]

Thorough...Thank you sir.

[@brianjohnson7872]

After replacing this board for the 5th time, I purchased a LED replacement tail-light assembly (both sides included) from Auto Parts Warehouse web-site for about $100. I've had no problems, since I replaced them 8 years ago, plus the blinkers are much brighter.

[@EddieRomero-mf2mq]

awesome ,I'm going to take that as advice and im looking into doing that upgrade asap , thanks for sharing that

[@mickjager5974]

Where did your LED assemblies come from? I looked at LMC and the LED ones they have are about $250 now. I thought about just putting in LED bulbs as they'd probably run cooler and not melt the bulbs base and socket and just put up with the faster blinking. They make resisters to put in line with them to fool the sensor and they would be less expensive than 250!

[@UFOGHOSTHUNTER]

Great video. My 95 takes two 1157 bulbs and 1156 for the reverse light. I can't find any aftermarket replacement assemblies with my setup.

[@mickjager5974]

Yeah I think they switched to the plastic based "wedge" bulbs and the metal "bayonet" style boards are few and far between. LMC might have some. www.lmctruck.com/1988-98-chevy-gmc/tail-light/cd-1988-98-tail-light

[@1Splat]

Get the OEM if you can. The Dorman circuit boards are shit. The metal contacts inside the tail light circuit board bulb sockets are real thin and if bent inwards won't touch the light bulb's metal contact(s). I've went thru 3 boards in 2 years because of this flimsy design. Another thing to check.... On my 98 C1500 I had no back-up lights. I replaced everything. Then I saw a switch located by the tranny underneath the truck. It's connected to the shifter on the tranny. I had to swap that out to get my back-up lights to work again., AS WELL AS one of the wires that goes to this switch was broke. I crimped it back together, taped it, and sealed it with silicon. Forgot to mention... If the brake bulbs aren't lighting try squeezing the circuit board and housing together on both sides of that middle bulb where the black plastic dots are. If the bulb lights then drill out those two plastic dots and use a 1/8" rivet in those holes. They'll squeeze the board together and fix your no brake lights problem.

[@higgsbuilt5914]

Thank you for this video🙏🏿

[@russellstephan6844]

Whenever replacing a bulb or working with an electrical connector, shoot a little dielectric grease in there to keep oxidation of the contacts at bay... That is, if you're going to keep a vehicle for more than 10 years.

[@rudyromero552]

Standing ovation

[@TailEndCustoms]

Man I’m having the same issue with my sons truck. I changed the bulb, comes on and off when it wants so I changed the board too. Same issue. So I’m guessing its a broken wire or loose wire somewhere. Pain in the ass

[@dustandshadows3179]

Try bending the little wires on the bulb itself so it makes good contact I'm sure it will solve your problem

[@chevy0771]

Great info. I just bought myself a 1998 Chevy C1500 2wd and the back running lights don’t work or the blinkers don’t work. My dad and I tested it and everything seems like it’s working but I think that board is bad.

[@joearrigo2290]

My problem is headlights on no brake lights or running lights change at of things still nothing

[@brianjacobsen5762]

Have 98 z 71 have turn signals but flasher fast on on side passenger marker lights out. The fuse kept blowing. blows tail instrument cluster lights headlight have running lights. The circuit board cause that. 146,000 it still has the factory grease in all the bulb plugs. This gives me place to start.

[@DrShock]

You might also have a short in the wiring harness. I go over how to check that in this video, I'd make sure that's all good first before chasing the board.

[@nonameisthename138]

How common is it for BOTH to go out at the same time??🤔 I was at a friend's house, and my lights were on. Noticed that I didn't have any tails or brake lights. Get home, and they're all working..hadn't checked it out yet. Its late and will do it in the morning

[@DrShock]

Seems unlikely for both boards to go out at the same time. I'd suspect an intermittent wiring fault first.

[@nonameisthename138]

@@DrShock Thats odd, nothing has been done to it recently as far as electrical goes. I've had the truck since it was two years old, and this is the first time something like that happened. I'm about to go check it out now...thanks for responding 👍👏👏👏

[@DrShock]

I'd suggest waiting for the failure to happen again, probably will be easier to trace it down being intermittent.

[@nonameisthename138]

@@DrShock Yeah, I have no choice now. It's been raining all day😡🤦‍♂️🤷‍♂️ But I will take your advice..

[@EddieRomero-mf2mq]

thank you

[@robbehr8806]

Good info. Regretfully, the replacements from China are junk. I just replaced one that is about 6 months old. I save the bad one and I'm going to find a way to direct wire around the circuit board. If I can pry the layers apart, I'll run conventional copper wire from the connector to the sockets.

[@kennetheugene60]

what do you have your meter set on to test the wireing plug

[@DrShock]

Just DC volts for what I show in the video, just to check that battery voltage is flowing thru the harness on each line

[@putheflamesoutyahoo1503]

very hard to find this info...seems google wants you to put in led lights.

[@elizabetholiver4758]

I am trying to replace the circuit board, but I cannot get the wires out of the old one. Do you know any tip I can try to get them to disconnect? Any advice would greatly be appreciated

[@DrShock]

If you're referring to the wiring harness connectors, and you've made sure to unlatch it, then it could be dried up insulation material in the socket. If so, you'll just have to wiggle it out slowly, to avoid breaking anything.

[@lucasr822]

Sweet!!!!!!!

[@DirtbikeDad]

I have a 99 Tahoe I mounted trailer lights to doors of rear for brake lights. They work great but recently the lights work when you barely touch the Pedro but as u push the pedal more to actually brake the lights go out. No brake lights. Any idea ??

[@DrShock]

Well my initial reaction to what you've wrote is the brake switch on the pedal. Obviously that's the only part that has a mechanical relationship to the brake pedal position. The switch may need adjusting, or it may be on its way to failing. But I'd start there.

[@DirtbikeDad]

DrShock no adjusting it’s the pain n the arse to get to with that lovely clip rotate up and off pin on pedal

[@DirtbikeDad]

DrShock main reason I mounted them was the circuit boards keep going out

[@ernestruffell5764]

I've got a 96 GMC 1500 single cab...I've replaced the multi function switch, brake light switch, and both circuit boards...my brake lights stay on constantly...I thought my brake lights weren't working but after testing everything , the problem is they're on constantly...what do I do?

[@DrShock]

This sounds more like a wiring harness problem to me given you swapped the brake switch already, so a short in the circuit is bypassing the switch. Have you tried the test at 3:40 yet? I would disconnect both boards and perform that test at each connector. Based on your symptoms I'd expect you'll read voltage without depressing the brake pedal doing so. I would be looking for either a short in the roof brake light, a bypass at the fuse box, or a wiring harness short to 12V on the wire that powers the stop lamps.

[@krisweber4853]

Thanks

[@ndeeeed]

Can this be the problem for me? So I’ve been chasing around this issue with my emergency flashers. When I have them on and simultaneously press the brake pedal, they stay solid as if they were hooked up to the brake lights. When the pedal is released. They resume flashing normally. I replace relays fuses and even a couple of harness & wires and the brake switch, but nothing has remedied it. Any ideas?

[@DrShock]

It is normal operation for the hazards to stop flashing when the brake pedal is depressed on all of these GMT400 trucks, except the Suburban. Working as designed for the rest. ;-)

[@andrettski8686]

@@DrShock Great info on both of your videos I've seen, I have a '94 Chevy p/u and have running lights, turn signals are good but no brake or hazard lights. I replaced the brake switch, after checking fuse and cleaned up ground to frame near the rear, didn't help. I'm at a loss. I do have a 2 way plug for boat trailer and RV.

[@DrShock]

Thanks. Reads like a wiring harness issue, I would get a meter into continuity test mode (you'll need a long length of wire to extend the meter lead) and start checking the harness from the front to back focusing on the brake lamp circuit first. Include the trailer harness extension in these tests too.

[@andrettski8686]

@@DrShock Thanks for reply, I'll let you know.

[@Intim31976]

Quick question perhaps you or someone else on here could answer. I have a 95 K1500 with a turn signal/brake light issue. When the brakes are applied the Left turn indicator on the dash lights up and also the signal in the front lights up. After a while it caused the Left turn indicator to flash continuously, extremely rapidly, weather the signal was on or not. I finally pulled the fuse for the turn signals because people always thought I was turning Left. I've checked the wiring from the rear bulbs all the way up through the frame, up under the hood and in through the firewall. From the fuse box to the brake peddle, I cannot find any place where the wires are bad. I unplugged the wiring for the rear lights under the hood and it still does it, I assume the problem is somewhere under the dash above the steering column. Just wondering if you or anyone else here has had a similar problem, if so what was causing it and what is the fix? Excellent video, by the way. Very thorough and informative.

[@DrShock]

If I had this problem I'd treat it as an electrical short. Removing the bulbs, removing the bulb circuit boards. I'd then use a voltmeter to check that each wire to each bulb has continuity with no shorts to ground or otherwise. A problem like this you may eventually have to pull the flashers and the turn signal switch and headlight/driving light switch assembly. The point is validate the wiring first, then add stuff back one at a time until you find the fault(s).

[@Intim31976]

@@DrShock Right, I started at the lights and worked forward through the wiring along the frame up to the firewall and to the fuse box and from the brake pedal to the fuse box. I disconnected the wires at the firewall, just under the steering shaft is a plug for the rear lighting, when unplugged at the firewall the Left turn indicator in the instrument cluster still comes on when the brake pedal is pushed. To me that should mean that the problem is before that plug, as everything beyond is disconnected completely, and can only be where power can still flow through the wires. I'm planning on testing everything I can later today, weather permitting...Central Minnesota has been very cold and wet lately making electrical diagnoses more difficult with everything wet. Thank you for your thoughts, hopefully we'll get it figured out..I"ll post what I find as I find it.

[@DrShock]

I'd try disconnecting the harness that goes to the turn signal switch on the steering column as another point of elimination. Definitely a short somewhere thats incorrectly bleeding in an electrical path from the brake lamp circuit. Sounds like what you're looking for is a point where the left signal is shorted to the brake lamp circuit. Take a look under the dash for any exposed wiring left over from any past non-factory accessory rework that could be shorting to turn signal flasher area as well.

[@Intim31976]

@@DrShock That is what I'll be doing tomorrow, weather permitting. My grandpa bought the truck when it was less than a year old, he sold it to my sister who then sold it to my daughter. To me it looks as if someone replaced the wiring from the firewall to the rear, the harness that runs along the frame, the pigtail for the trailer lights (which I removed due to another short) and to each side all have aftermarket tags on them. This would of been done before my grandpa bought the truck when it was only a few months old. I was the mechanic for the truck since he bought it, the person he bought it from claimed he never had any problems with it, he is a local who we all know well. When he sold the truck to my grandpa he bought a 2500 silverado. I started to pull the bottom of the dash apart and I can see on just before the column goes through the firewall the wires coming out of the brake light switch appear to have been worked on before. Without digging in more I cannot see exactly what was done or if that is the problem, but at least one of the wires has been partly stripped and soldered. I believe I'll have to drop the column to get at it, so I will disconnect the wires you mentioned first just to rule that out before dropping the column. I am currently working on that, 2 of my old John Deere's, our 04 Tahoe (electrical nightmare), my 99 silverado, and remodeling our house. It'll be nice to get a few projects done so I can go fishing with my boys, hopefully soon. I'll let ya know what I find, as soon as I can get back at it. Thanks again, I truly appreciate you taking the time to share your thoughts with it.

[@SibRevs]

Is there any way to effectively repair the board? Re soldering joints and such?

[@DrShock]

Replacements are not that expensive, and would be cheaper than the cost in time to attempt that. The circuit board assembly is molded together at the time of manufacture. Once you let moisure in there, it's going to corrode in short time (which is what I suspect eventually gets them anyway after 10 years or so).

[@trevdawg6.6]

Did the chime go off on the dash when the headlight switch was on? And did your tail lights or anything else work?

[@DrShock]

Everything else behaved normally, this problem I recorded here is particular to the tail light circuit boards developing trace defects with age.

[@SeattleSuburb]

Would this at all be applicable to the 94 model year? I know its mostly interior and engine/transmission differences, but do the 94's have a circuit in the tail light like that? Im getting this issue where both my reverse lights come on just for a split second while switching into reverse. and then stay off while in reverse, or they work just fine. Would love if its just the circuit board and not a ground or neutral safety switch, or wire. I haven't tested them yet but I will tomorrow

[@DrShock]

Yes it would, I updated the video description as this part was used as far back as 1988 on pickups

[@SeattleSuburb]

Nice, thanks for the update. My issue actually ended up being the little reverse light switch on the steering column. I couldn't find a video ANYWHERE on how to remove it, but after just messing with it enough, I was able to get my reverse lights to function correctly again. But I love learning about these trucks so the info in your video will server me well, no doubt.

[@deejayasap]

Would this cause both brake lights to fail?

[@DrShock]

Sure if both boards went out, kinda unlikely to both go at the same time tho.

[@alexfreeman3281]

ahhh man 🤦🏽‍♂️ i just bought new headlights and taillights and i realized my ticking and light was faster then before i thought it was maybe cause they were new but now i know it’s only a future problem shake my head 🤦🏽‍♂️

[@armandomendoza3167]

Is it a comon problem that also. When applying the brakes while having either left or right turn signal. The the blinking light stops on a solid lit light. When applying the brakes?

[@DrShock]

Having the turn signal behavior interrupted simply by applying the brakes is not normal (most drivers are going to be sitting in a turn lane with the brakes applied and the signal engaged). It would be normal for some vehicles for the hazard flashing to stop when the brakes are applied, but not the turn signal.

[@cybertechcomputerz]

I am having that same problem, did you find a solution?

[@gusrobbins4682]

Ok I gotta question I got a certain set of bulbs that work right it’ll have brake lights and blinkers but it won’t turn off why’s that

[@DrShock]

You mean that its staying in the parking lamp mode? Tail lights continuously on, but still blink and get brighter for braking?

[@gusrobbins4682]

@@DrShock yes that’s exactly what’s happening

[@DrShock]

@@gusrobbins4682 Sorry for the delay responding, I missed this comment earlier. You'll need to trace the wiring harness from the tail forward for this one. There's either corrosion or rodent damage, or a problem at one of the ground points leading to this sort of behavior.

[@Devo1987]

[@yourface691000]

my brake lights and running lights work but my back blinkers do not. I've replaced the beard and still nothing so what do y'all think it is. if you can please let me know thx.

[@DrShock]

What were the results of checking the wiring harness as shown in the video during turn signal activation? If the harness checks out, on both sides, and the front signals work (eliminating the flasher relay) then I'd have to say it's the circuit board in the taillight still, or the bulbs.

[@yourface691000]

@@DrShock I haven't checked the voltage of the wires yet but yeah I believe it's the bulbs

[@johnnyriner5337]

same issues except both sides are out on my gmc. how often do both go out at the same time?

[@DrShock]

I've not personally ran into both boards going out but I have heard/read about this possibility.

[@johnnyriner5337]

@@DrShock thanks for the quick reply. i replaced both boards, didnt fix the issue. I am at a loss right now

[@DrShock]

Did you do the wiring harness electrical checks, on both sides?

[@cristobalsilvalillo1845]

Hi, I have a similar issue but I already change both sides boards and it continues. If frontlights are switched on tail blinker don't work only front ones. If i frontlight are switched off, tail blinker and front blinker work but at a fast pace as on your video. Also break lights only work if front headlight are off. Once I switched on the breaklights go off. Do you know what may be happening?

[@DrShock]

I would disconnect both the rear circuit boards and start checking the wiring harness with only the front bulbs installed. I show in the video what each wire color is for the rear harness connectors. If you're still getting the odd behavior then you have a bad ground or corrosion problem in the wiring harness and/or one or more of the illumination switches for brake/turn signal/lamps. Fortunately none of this stuff is computer controlled in these model years, so its just basic but time consuming electrical troubleshooting. You want to get down to the basic harness testing, then unplugging switches. I'd unplug headlight switch and turnsignal stalk and check just break switch. Do I get brake lights only with brake switch? Then add in turn signal, can I do turn signals with and without brakes? Add back in headlight circui last.

[@19491Tommy]

I have the same problem.... I have watched several videos tonight on this. Tomorrow I am going under the rear of my vehicle, as it seems that most problems are contributed to a bad ground located on the rear .

[@wadestewart1549]

What if no power to the DS . And blinking fast. Back is ok

[@DrShock]

Blinking fast on the instrument clusters green turn arrow lamp is an indicator there's an open circuit in the turn signal path (either front or back). Usually an indicator of a burnt out bulb in one or both so check that first. But like in the video can also be caused by the rear circuit board going defective internally. When you say no power "to the DS" - what do you mean here?

[@Pursnikity_20022]

I've replaced one already when i have my hazards on, all the lights flash could it be a flasher relay instead?

[@DrShock]

Sounds like a short circuit somewhere, what happens if you disconnect the board you have not replaced yet but leave connected the one you did? I'd next disconnect both boards, and meter out the harness to help confirm if the problem is in the hazard switch or elsewhere along the harness itself.

[@Pursnikity_20022]

@@DrShock ill give that a try, thanks.

[@Pursnikity_20022]

I’ve replaced both circuits. Now the two bottom flash an not the top. I’ve replaced a relay switch under the dash. Still nothing though

[@DrShock]

Does the turn signal switch action behave as expected? When you metered the harness lines out like in the video with both boards disconnected, while the hazard switch is enabled, are you seeing pulsating voltage (flash action) on any of the other wires?

[@Pursnikity_20022]

@@DrShock i went ahead a replaced the multi switch just because, but still the same problem i just need to look for a loose ground or something, that's all i can think of .

[@isaiahdaquioag8708]

What about when i hold the brake with the hazard on? While holding the brake and hazard on, the hazards dont flash, they only work when i press the brake

[@TheTronak]

That's normal.

[@Nomadcreations]

Isaiah The Brake Lights Cancel out the 4 Ways Circuit

[@kyleniedzielski3995]

Does anyone know if the tyc ones are better than dorman can’t find oem driver side 😔

[@DrShock]

You could be better off pulling an used OEM board from a salvage yard model year 2000 or so C/K truck than using anything aftermarket.

[@ghost676kdheg]

I put new bulbs in and new boards it did not help but thank you

[@Jayj93pgt]

i have a similar issue, but my hazards don't flash if the lights are on. not my brake lights, but just my regular running lights. anyone know what might cause this? and I too have gone through 3 circuit boards on the left tail light. the right tail light still has the factory circuit board from 25 years ago

[@DrShock]

If I understand you correctly, your hazards don't flash if you have the parking lights on but work correctly otherwise. And the parking lights work ok by themselves. If that's correct, I'd pull rear circuit boards from both sides and retry hazards to see if just the fronts work. If success there I'd be looking for a shorted bulb or board connector on one or both sides. If they still don't work I'd pull the front parking lamp assemblies and start checking all four harness connections with a multimeter. I show in the video how to check the rear one, for example.

[@Jayj93pgt]

@@DrShock thank you I will do some testing and see what I find out. Someone did have trailer brakes installed on my truck at one point so hopefully that wiring isn't causing problems somewhere.

[@mickjager5974]

The blinker and brake are the same bright filament in the center bulb. So if you are just braking and have the turn signal on the only brake lights you have are the one on the non turn side and the 3rd brake lights. On the turn side it only functions as a blinker. Kind of a silly arrangement in my tiny mind.

[@GwinnettLawns]

The 89 has a different kind of board and used different bulbs.

[@DrShock]

That's odd because the GM parts book shows 1988 up for all pickups. But not SUVs. What model truck do you have?

[@GwinnettLawns]

@@DrShock I have an 89 K1500 Silverado. I still have the factory circuit boards and they use the round bulbs with the pins on each side not those spade type bulbs.

[@DrShock]

Ah ok I see what GM is saying. Is your wiring harness connector the same as the 1998 one in the video? Because I suspect it is and GM is expecting customers to upgrade to this board for 1988 and 1989 (the parts note I have says this circuit board replaced the previous one on July 1st, 1991). I updated the video description to point this difference out, thanks for the comment!

[@michaelsherman4203]

If I replace the light bulb still no tail light then what I do

[@michaelsherman4203]

I have a 2000 Chevy z 71 truck

[@DrShock]

What did you get when performing the check I showed for the voltages at the wiring harness?

[@thelastdon3607]

If u tried all of that and it still don't work what could it be

[@DrShock]

If it's not the bulb(s), and not the circuit board(s) after going thru this video the brake lights are still inoperative / operate incorrectly then it's time to check the wiring harness. See some other comment threads in this same video for previous discussions on this. But you're going to need to disconnect both tail light circuit boards, and disconnect the brake lamp switch and start to debug the harness one connector at a time one wire at a time looking for shorts or opens.

[@24ozz]

Can I use a test light?

[@DrShock]

You can, but you may not be able to _accurately_ tell if the voltage is below the value needed (which can be caused by corrosion in the wiring harness increasing resistnce in the copper wire).

[@ImARedFreakinTowel]

What if both sides are acting like this?

[@DrShock]

I've never seen two boards go at the same time, but I have seen them go out within a month or two of each other so I guess its possible. But if you get the results I show in the video doing the same tests, it's the board. Pretty cut and dry diagnosis.

[@keithbartlett7679]

I want to find a way to wire this board up so that you have both lights illuminate for turn and break.

[@MrBowNaxe]

Just started having an issue with my Suburban tail lights... Reverse lights come on when I turn on my running lights. So what's my first move? Go checkout Dr Shock's library! I think this might be my issue. Left turn signal started flashing fast about a week ago. Today the reverse lights came on when I turned on my running lights (Previous owner had daytime running lights disconnected). I was about to install back-up camera and this problem showed up. So, first things first. Any suggestions?

[@DrShock]

Something in the wiring harness I would suspect, checking the voltage and grounds at every connector end thru all lamp switch positions would be the first start.

[@MrBowNaxe]

@@DrShock thanks. I have to find my volt meter leads... Don't know how/when they got separated! Might just be buying Kofi soon... Need to backtrack and see if messing with my trailer connection is the culprit too.

[@MrBowNaxe]

FOUND IT! I knew something with the trailer light connection must have caused it. Apparently, when I was putting the plug back into the harness, the center screw pushed the "reverse" wire into the power and running light pin... Whew! new plug on the way.

[@imanigr14]

My blinkers work, my tail lights work , but my brake lights will not light up

[@DrShock]

Could be what we cover in this video, but when it's happening on both sides at the same time suddenly more likely something else. I'd still check bulbs and measure voltage at the taillight harness on both sides like I show. If you are not getting voltage when braking, check the brake switch at the pedal next.

[@Pops5]

I have a 2000 GMC and it has no circuit board in the tailight. Right turn signal… front blinks fast, rear not at all. Guess GMC did something different in their tailight design. I dunno.

[@DrShock]

I would guess your 2000 is the new body style truck that came out in 1999? There were still old body style (OBS) trucks in 1999 and 2000 for the 2500 and 3500 work trucks where this video would still apply. But no, the new body style was a different design than I'm showing here.

[@meateorman4191]

My blinker bulb is glued in 😓

[@DrShock]

It didn't roll off the GM assembly line like that ;-)

[@napieraustin]

Meateor Man Could be wrong but I bet that’s not glue probably dielectric grease dried up.

[@mickjager5974]

I'm guessing melted in.

[@alexis_1503]

how about when your reverse lights turn on when you brake can someone help ?

[@DrShock]

Electrical short. You have to attack with a process of elimination. Presuming your truck year fits the range this video covers, I would first disconnect both rear circuit boards (L & R sides) and check the wiring harness as shown in the video. If the harness shows voltage on the backup lamp circuit when braking your problem is not in the rear housing circuit boards, but rather "forward" of them. I would next get the schematic from the service manual and start tracing back to the neutral safety switch (controls reverse lighting) on the transmission to find the short.

[@alexis_1503]

found it my dog bite the wiring harness where it connects under by the spare . but there's this blue that connects to the m wring that goes to "forward" part of the truck

[@alexis_1503]

can i cut the blue wire from another truck and just have it like that and connect that blue wire to my truck

[@DrShock]

Well if you're sure it's just the wiring yeah you could salvage that from a donor truck. You could also just use the same gauge wire from anywhere quite frankly. Just be sure you insulate the splice properly from the elements.

[@alexis_1503]

the blue wire comes in the package of the wire harness that come from the "front" but it separate it's not connected to the connector hits by itself connected to something else , but with my truck it doesn't have the blue wire that the donor truck has

[@ferrariguy8278]

Uug.... I have an 89 with the original bayonet style.... and it looks like I'm going to be forced to change to these - pieces of junk - The Bayonet plate numbers are 16507051 and 16507052 but afaikt are NLA entirely.

[@MrMimoresdj]

What size screw is it?

[@DrShock]

That I don't recall, ¯\_(ツ)_/¯

[@EdgarBriceno-st7dp]

Has el vídeo en español

[@couchrider6228]

Hyp er flash !

[@oilymelon]

replaced the left blinking bulb works now but when i turn my regular lights on same bulb does not come on only when i brake or blink it does. Would it be the circuit board?

[@DrShock]

So you repaired your turn signal with a bulb replacement, but now the marker lights are not working. Just turn signal and brake. It could be the circuit board, but I would check the wiring harness like we did in this video to be sure first.

[@oilymelon]

@@DrShock alright thank you