How to Install a Secondary Fuse Box Quickly and Easily (Car Auxiliary Fuse Box)

If you have a ton of accessories (dashcam, gauges, footwell lights, auxiliary electronics etc) and struggle to splice into a power source or find a ground bolt every time you install something new, this mod is for you. This is a simple process that allows quickly and easily connect and disconnect accessories to their own fused power sources with no cutting or splicing required. Watch as I run through how to install a secondary accessory fuse box that runs directly from the battery but does not draw power when the car is off on my Legacy GT. You will need a fuse box, SPST relay, and some lower gauge wire depending on how much power you want to run to the box.
Things I used:
Fuse box - amzn.to/3gj8YF0
SPST relay - amzn.to/2LVYFJ0 (this is a 6 pack but you only need 1. Any brand is good but ensure it has the wire sections and is 12V with high amps)
Useful heatshrink solder connectors - amzn.to/2wPpB8U
As an Amazon Associate I earn from qualifying purchases (but this doesn't cost you anything at all).

[@ClaytheBMXer]

Not sure if I missed it, but the power feed from the battery to the new fusebox should be fused at the battery at the amperage capacity of the fusebox with the accessories used. If the big positive cable running through the fender gets shorted, or one of the lugs on the box gets shorted (example: an accident), then your battery is directly shorted to ground! Cool video by the way!

[@petetherealrelentless6542]

100%. TBH I found running the wire through the fender a bit harder than it needs to be.. I always go through the firewall grommet.

[@green3488]

So 40A?

[@ClaytheBMXer]

@@green3488 It's been a year since I've seen this, so I don't remember the scenario here. But you want to calculate the correct size fuse for the current draw of that circuit. If you have several things on the circuit (power being supplied to an auxiliary fusebox), you would need to determine how many of them could be on at the same time and the potential total Amperage draw of all devices (or alternatively of what you might have on that junction/box in the future). Then you can calculate what to fuse your fusebox at. Don't forgot to account for wire gauge, connections, etc. so nothing melts or catches on fire even if you use the correct protection devices.

[@green3488]

@ClaytheBMXer Yeah, I knew that much. Just wondering what final answer is likely to be. Like, if it's all set up to handle 40A or not... Can 14 AWG handle 40A? What about 12 AWG?

[@green3488]

@ClaytheBMXer Google says 12 AWG is usually rated at 20 to 30A depending on insulation, while 14 AWG is about 15A.

[@EZ-viewing.]

You’re a very well informed gentleman who does not mind sharing his experience. I’ve been searching for this a very long time. Thank you for your efforts.

[@RPGarage]

Much appreciated thank you

[@nuff8846]

As someone who's spent at least 100 hours trying to learn this shit from Google, even though I'm a visual learner, thank you. I get tunnel vision and struggle otherwise. So, seriously, I appreciate the video!

[@coreyblitz2000]

What a man! Gotta love subaru people for always coming in clutch with clear answers for my questions.

[@malachiclifton8795]

This is a nice high quality video that was very informative. I appreciate your straight forward explanations paired with your good videography of exactly what you were talking about.

[@pujolsh8tr]

Thanks for the great video. This was exactly what I've been trying to find. A very simple explanation on how to install an extra fuse box for small accessories.

[@RPGarage]

Glad it helped!

[@joemzd]

I gave you a thumbs up as soon as you corrected yourself from "just as good" to "just as well". Good job!

[@losrodriguez4212]

I’ve have been looking for a video to add a fuse box like this without wiring a bunch of relays and had a hard time finding one. Thanks !!

[@RPGarage]

Glad it helped!

[@blackterminal]

Im working on a electric car project and this video was helpful to me for adding a fuse box. Thank you

[@johnevans737]

Absolutely perfect then I was a technician for Chevrolet for 10 years I know how to replace and repair anything on a vehicle up until 2016 but to be damned I could not figure out how where and why I could put my new fuse box that I added after adding two optimum batteries a 200 amp alternator and multiple accessories like backup camera Android touch screen radio front cameras and plow heated cameras so for when I'm filing and many other items with your simple advice and good ideas I was able to find the perfect spot in my truck where the wires reached easily looked gorgeous and did what I wanted to do thank you so much once the interior is done I'm going to take my beautiful truck which is not so beautiful now to the body shops maybe and turn her into a show truck

[@luiso6827]

Awesome video! Ppl be sure to use his link in the description to purchase this product as a thank you! Thanks for making this video.

[@dajur1]

Nice video, this is exactly what I was wanting to learn. Thanks! I just wish there was a fuse panel with 2 fuse sections so that I could have constant power on 1 half and ignition power on the other. Well, I guess I'll be buying 2.

[@stephenbrook9085]

This is excellent advice! I was watching this for my VAG car but i also have a legacy 😅 Thanks this will be great help

[@draftnotion]

Great video, I am adding a wideband afr gauge and will do this for the power

[@70MUSTANGMAN]

I appreciate this video! I bought the exact same fuse box off Amazon so this helps!

[@anomalous9448]

Thank you for mentioning 12 gauge wire to power the fuse block. No one else speaks to wire Gauge. How to videos should cover all bases.

[@bradleyhawks8689]

Very well put together video and easy to understand the info. Thank you!

[@zachster2016]

I'm a beginner. As in I watched like 2 other videos before you, so I had a slight understanding of what you're talking about, though I didn't catch what you meant by you led a wire through the fender and then for some reason your new fuse box has its own positive and negative to connect to and then I was confused why you even needed to do any of that when you have an interior fuse box, I've got a lot to learn, hopefully quickly lol

[@sorodaxu-]

You are a life saver. Thanks I appreciate your time and video. 👍

[@DJLIBERATORE7]

Very well done. Thanks for taking the time to do this video!

[@jona3294]

Surely when you tap to an accessory that only switches on with ignition (and engine running), you won't need a relay as that is basically your "automatic switch" since the accessory that you tap into ONLY switches on as you turn the key in ignition?

[@tomskimcdouglegaming806]

depends on the amperage of the accessory.

[@rameljeferuiz]

This is so cool, i want to add led lights to my 79 ford

[@joserhdz85]

Thank you so much! Great explanation this is what I needed

[@chrisgraham2904]

You should note that the use of the relay allows the new fuse panel to only have power when the ignition is in the ON position. If you want power at the fuse panel continuously, no relay is required. More importantly, with or without the relay, you need a fuse in the power supply line from the battery. If you using #12 Awg wire off the battery, you need a 30 amp fuse installed as close to the battery as possible to protect that power supply wire from overheating and causing a fire. The wire size off of the battery and the fuse protection will depend upon the total number of amps drawn by the circuits of the panel.

[@green3488]

How did you come up with 30A? Is it because using more than that with 12 AWG is bad? His relay will support 40A. So should bigger wire be used to get more than 30A? Thanks.

[@tombackes9557]

Great and easy to understand video.

[@mjb4ever]

Great explanation and very easy to follow.

[@michaelmorris6575]

Great video! Thanks for sharing.

[@NoSlackZak]

Great video. Thank you.

[@OscarGonzalez-cw9hm]

The relay is necessary? Or just a positive source to the new fuse box ?

[@Caza390]

What if you wanted to add multiple ones of these? Second question is what if you wanted something to be a constant?

[@samm.2213]

Why do you need a relay in line between the battery and auxiliary fuse panel?

[@rgomez86]

So your accessories don’t drain your battery if you accidentally leave them on. Turning the car off also removes power from the accessories.

[@UntiI117]

Because then whatever you have connected to the fuse box will be on 100% of the time and wont turn off

[@black11189]

@@UntiI117 but if you already turn off the key, that mean there no current on the acc, so the fuse box shouldn't get current ??

[@UntiI117]

@@black11189 but the wires to the fuse box are going straight to the battery, so even if the key is off it'll still be powered. So the relay is there to disconnect the circuit when you turn the key off

[@rjensen4896]

Awesome video, thanks for sharing! Quick question: If you don't have any accessory fuse outlets, how could you wire up the triggered positive on the relay? I'm trying to install an extra box on an old car with glass (AGC) fuses.

[@raoulraoul7129]

It would not be recommended to mount a fuse between the battery and the new fuse box?

[@IProHeadhunter]

Did you add an inline fuse between the relay and the battery? If so what amperage

[@helmkaj]

Or breaker?

[@daniellee100]

Yes, add a fuse the same amperage as the relay between the battery and relay

[@BigDOOMson]

@@daniellee100 how'd he do that if he got power from the stock fuse box to the relay and then to the new fuse box?

[@polosavage1]

What if you wanted to hook up a device to a constant power source so that it works with the car is off and on instead of a accessory stores that only works when the car is on

[@damiannicotera2809]

I was wondering if anyone has asked but what size fuse did he put in the fuse tap

[@dptp9lf]

if you have room it's nice to have a switched and unswitched one

[@macd6351]

Good class!

[@the_wilkini]

Nice video but I don't agree with using the same colour wire for -ve & +ve connections.

[@macd6351]

Could I wire the fuze panel directly to the battery and have dash switches to relays to the fuze panel to power my accessary lights and components?

[@williamvaladez3149]

Why do you need the relay for??? Can we do it with out the relay

[@binaryglitch64]

I'm looking for a way to add a fuse receptacle to one of the empty spots in my existing fuse box. Is this a thing? My search only shows fuse tapps and add-on fuse boxes, which are not as clean as what I'm trying to achieve.

[@BilderbergCEO]

Thumbs up for "just as well" :)

[@rameljeferuiz]

Excuse the stupid question but what will be the difference Between having a relay and inline fuse

[@BBBBBBULABOG]

A fuse is a bridge that will collapse if too many people goes to the other side. This is to protect the wiring down the line so it does not burn. A relay is a switch in a switch. What this does is bridge the gap between the battery and the auxiliary fuse box ONLY when the relay itself is fed power (this can be tapped from the original fuse box, mainly the accessory because it is only on when the car is in "on" or running. So, Battery > inline fuse (with amps same as relay) > bottom blade of relay. Left blade of relay to ground Right blade of relay to ACCESSORY fuse from the original fuse box. Top blade goes to the new auxiliary fuse box

[@randomname3665]

What’s the difference between putting the negative on the new fuse box to ground or going to the negative on the battery?

[@raffie9526]

Great video !

[@shaunmoeller3288]

I just had my vehicle stolen... police found it in 2 days no damage was done except they tried to paint it... I was thinking about adding a hidden fuse box inside the vehicle and just pull out a couple relays to prevent the car from being stolen but keeping the original fuse box with all relays and fuses under the hood that way if they did look under the hood and check fuses it would look stock... just not sure how I would hide it in a 96 Cherokee being there's not many hiding spots

[@asd67lkj]

Newbie question.....which fuse did you hook into to have power on "Accessory"... PS I have a Toyota Hilux... (Oz) Liked the way you set up so power only come through when you turn the ignition switch on...

[@UntiI117]

The best way is usually the radio fuse.

[@ramilmarbella7559]

for me i go on cigarette socket

[@jesseportillo324]

Very informative...question. how would you hook a switch to turn on and off the lights 🤔

[@UntiI117]

Instead of running the power wire straight to the fuse box. Run the wire to the switch, then to the fuse box

[@jesseportillo324]

@@UntiI117 sorry. I meant from your diagram ...how would you hook up a rocker switch to it. I assume the switch would have to be connected to the the relay ? Is this correct?

[@ramilmarbella7559]

@@jesseportillo324 dude he connected it the acc by key that means when u turn the ignition on, it should have power...

[@calrs682]

Nice work👍

[@AnZ85]

Hi. I would like to ask. So, from the relay. Red= add on fuse acc box + Blue= from direct 12v battery Black= ground White= main acc fuse which off when the key is off? Am I right?

[@jd8223]

What gauge wire did you use to ground the new fuse box to the car? What if you wanted to add a toggle switch to be able to turn the access of controls on and off?

[@georgeowen3506]

I feel like you are missing a fuse on the relay power feed line.

[@AJFAful]

Hi, nice job. What other way would you recommend to achieve the same outcome, but without taping into an accessory power source (Having an independent 12v ignited not constant fusebox).

[@RPGarage]

The reason I used the relay and accessory tap is because I don't want the fuse box to stay on when the car is off or it will drain my battery. If you just want an independent 12v source you can just run a positive and negative wire to the battery directly and use a switch mounted inside the cabin somewhere to turn it on and off but you risk forgetting it on when you leave the car. If you do that you just need to put a fuse in the positive line and you're done. Not sure if that's what you meant

[@AJFAful]

@@RPGarage Thanks for the fast reply. I do have the same concern as you, I only want the fusebox powered while ignition is on (Acc Position). But I want to achieve this without having to tap into an ACC fuse, I want something else to trigger the relay (if a relay will be used in this hypthetical other setup).

[@black11189]

@@AJFAful one year after what did you do ?

[@erikpayne8202]

@@RPGarage thankie

[@zaheersarwar7815]

I'm putting an led beacon light in my van, which needs to operate with the ignition off. I won't be using a relay. Won't need it..

[@HotSauceIgnited]

Is it alright if the bus bar is grounded back to the battery?

[@RPGarage]

No it should not be grounded directly to the battery. Use some part of the frame of the car

[@trevorbelmont4633]

Do you really need the Relay between the Battery and the fusebox?

[@BBBBBBULABOG]

Hi. The bottom blade of the relay should be wired straight to the battery with an inline fuse with the same amperage as the relay itself. Left goes to ground - this can go to any metal part or straight to battery as well. Top blade will be wired to feed the auxiliary fuse box. RIGHT blade goes to the ACCESSORY fuse from the original fuse box so when you turn the key to "ON" or "Start", it supplies power to the RELAY which will close the gap between the bottom blade and top blade = power to the auxiliary fusebox. So yeah. Without the relay, your auxiliary fuse box is continually drawing power from the battery which will drain it.

[@JuanGomez-ih3zn]

I need to put on my car a New Fuse box Can u do ... Where are u Location???

[@IDABAYAREA650I]

*So if im making a custom interior dome light, if i wire them directly to the fuse block, do i need to add a relay? Id like it to be hot at all times due to being turned off by the original push style button you use to turn it on, like from factory when you open the door the lights come on*

[@jhsubarurepairsandmods8712]

Nice solution. Is your steering wheel completely wired up for the audio and illumination?

[@RPGarage]

kzbin.info/www/bejne/iZ7Yo4xvbqeFp80

[@knight3131]

Wouldn't this cause parasitic drain of the battery ?

[@johnlee1009]

Why go through the trouble of routing every ground back to the bus? If the chassis is grounded, why not just ground it wherever? I'm adding a lot to a classic car. There's a lot of exposed metal for ground.

[@RPGarage]

If you've got a lot of easy metal in reach to ground to that's completely acceptable. In my car it's annoying to try and find a good ground in different spots hence the ground bus. Easy and reliable, especially for accessories with paired +/- cables

[@knight3131]

You don't get parasitic drain ? Also can the ground from the fuse box be connected to battery negative or it has to be to the car ?

[@RPGarage]

Have you watched the whole video or read comments? All of these questions are answered

[@joeyweijts2003]

My friend please solder connections with an iron those connecting things will melt eventually

[@RPGarage]

Have you ever seen this happen? I've ran these for years and never had any break or melt.

[@AlexT-md9df]

If you are running from battery to rocker switch to fuse box do you still need a relay? I’d like to run lights even when car is off being able to turn it on with a rocker switch in my car

[@averyely9741]

I May be wrong, but i think you can run a positive from the battery to the switch, than from the switch to the fuse box. You could then ground it out like normal

[@rodolfomunoz6016]

hi how mich amp did you use on the fuse tap to the relay? is it 30amp? or what should be

[@teresodorado8838]

Great video!!! Only question I have is do I need a relay for each individual accessory? Such as led light bar and or fog lights.

[@josepreciado5312]

I don think so know that he added the relay on the 2nd fuse box

[@mirafelizav.hernandez8341]

He only put a relay for the fuse box. So installing accessories such as led bars all you need is find out how much amp does it need for it to power. Not too much amp because it will burn your wire or less amp will blow your fuse. Just the right amount of amp fuse for it. Usually 3led lights will pull 0.02amp. So do the math. Good luck

[@twigglykevin]

Adding a relay eliminates "parasitic draw" correct?

[@twigglykevin]

When connected to a switch... Ie ignition

[@ChrisP-l3h]

You should not use 12 gauge wire on a block that should take bigger amperage that block is a 100 amp block it should be 10 gauge wire at least

[@bongski1797]

Whats the size of the wires?

[@green3488]

12 AWG.

[@xobaby3862]

♥️

[@carlossdb2]

Where is the inline fuse located on the wire coming out of the battery?

[@RPGarage]

I put one on later after the video. Given that the wire that comes from the battery goes to a relay and then everything else is fused, really the only way there would ever be a short is if that wire from the battery somehow contacts the frame but you're right, having one there is best practice.

[@TheEpicShadow]

@@RPGarage What size fuse did you run from the battery to the relay?

[@surfingfire479]

I have a 12-way fuse box with a 100amp max output. Would I hook it up just like this? If so, then what type on gauge would I use. I have a relay of 12v 120amp max.

[@Adam-gn4oo]

Just to be clear if I wanted the fuse box to always be powered I just wouldn't us a rely correct

[@RPGarage]

Correct

[@black11189]

If it already on the acc why the relay ?

[@RPGarage]

So power comes directly from the battery instead of through the ACC fuse

[@black11189]

@@RPGarage but in your case it already on the acc

[@Mach1Chriss]

The Vid was great but my god your index finger nail kept making my stomach upset did you drop something on it .

[@brennonbourque8899]

Bro your fingernail.....

[@fun6243]

This you tuber texted me and wants a video on your fingernail.......

[@joelikesconverse]

nice video man, but you skipped past a lot of the stuff that would have been helpful to see.

[@RPGarage]

Like what?

[@joelikesconverse]

@@RPGarage all the bits you done when the camera was off.

[@PBS-nm1uu]

if you really did your homework you will know you used the wrong wire for power.

[@RPGarage]

Oh damn. Guess it won't work.

[@xxxxxGhostBoyxxxxx]

Interesting setup. One question. Why do you need a relay for the secondary fuse box? Can it be attached directly to battery without it?

[@anonymousperson4363]

To make sure all connected devices are off when the ignition cylinder (switch) is off.