Final Check on the MGB Wiring Harness - Almost There!

We’re wrapping up the 1980 MGB wiring harness install today. It’s time to check out each circuit to be sure that everything is working as it should. Before we get started, we’ll discuss how to hook up the new radio and USB port so that we aren’t overloading the wiring. Then, with our battery test fuse in place, we’ll start in the cockpit checking the gauges, dash lights, marker, headlights, map and boot lights. We had a few minor hiccups that we show you how to easily fix. Once we know that all of those are working as expected, it’s time to finally turn the key…but only to the on position, it’s not quite time to try to start it yet. So we then can move on to test the wipers, the blower fan, turn signals and hazards where we again find a small issue. Then we check the new radio, USB port, discuss the testing procedure for the fuel gauge, and find out why the back up lights aren’t both working. Last to check at this point is the washer pump and we share some advice that may keep you from having to replace it. After removing our test fuse at the battery, only then do we turn the key to start…and nothing happens. So it’s time to diagnose again and with a quick fix and hooking the fuel pump up, it roars back to life. But troubleshooting isn’t quit done yet. We listen for the anti-run on solenoid then go back in the cockpit to check on the tach, and other gauges and discuss the reason why your gauges may be reading high. We need to get some heat into the engine to check the temperature gauge and to be sure the fans are coming on and turning off at the correct temperatures. After finding the temperature gauge is still not working, we discuss the differences in the temperature sending units between pre, and post ‘77 cars, and how to test them. Before we’re done, on these late B’s there is one wire we want to leave disconnected, watch to find out why. Now that we have tested everything, only then is it time to finish carefully mounting the dashboard and neatly tying up the wires, it’s very important to take your time on these last steps because it could be the difference between a successful install and melting down your brand new harness.
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[@americanpatriot2422]

Always an outstanding video and presentation.

[@MGB-learning]

This is an outstanding video that clearly covers the final stage of checking the installation of the new harness. The video also covers all the checking procedures and possible issues. Thank you!

[@michaelstoliker971]

Ah, the reliability of Chinesium reproductions.

[@MGB-learning]

You are absolutely right. The poor quality aftermarket parts from both China and India (just list two) are terrible. I always look for Old stock OEM whenever possible.

[@bladerunner6282]

i've got three british cars and finding a temperature sensor that fits AND provides the right voltage to match the gauge so as to create a modicum of accuracy is a guessing game AFAIK. for the better part of a century their outward appearance hasn't changed much, in fact they're practically identical, but the threads differ, the amount of threads differ and the voltage they produce for a give temperature differ... smh.

[@mgbgtguy]

You also have to remember that the voltage to the gauge will change the reading as well as the resistance range within the sensor itself. The gauges can also be adjusted as well, but for most people they should probably not try to.

[@oxfletch]

You mentioned the tach taking a few seconds to start working - mine does that every time. Any idea what the cause of that is & if it's fixable?

[@mgbgtguy]

I’ve never had a customer who actually decided to fix that. My guess is it would take a rebuild of the gauge to fix it, but it is a very common issue

[@americanpatriot2422]

​@@mgbgtguyI thinks the issue is caused by years of condensation inside the house. The internal connections have corrosion

[@americanpatriot2422]

Broken exhaust hangers and brackets can lead to cracking of the one piece intake and exhaust manifold.

[@mgbgtguy]

Yes it can, and this one has already been brazed back together once. The current owner just bought it and will likely fix that along with a couple other things

[@phmiller25]

I am resto modding a 1974 MG Midget. I like the dashes though of the 1965, 66, 67 Mark2 style. I just wonder how difficult would it be to modify the wiring harness for. Or is there any recommendation you would have concerning this?

[@mgbgtguy]

Lots of owners of MGB's have retrofitted the pre '68 dash into later cars, so it is doable (yours would actually be easier as the early/later B scuttle is different requiring a filler panel). You just have to look at the wiring diagrams for both the '74 and the '65-'67 cars to determine the wiring differences, and adjust accordingly to make it all work. I honestly haven't looked close enough at those year differences to know if the mountings changed (not nearly as many Midgets come through the shop as MGB's) but I would think they are likely the same/very similar as they really didn't change things like that if they could design around what was already there to reduce tooling costs.