Dashboard Restoration
Unwiring
This car has some electrical issues. At some point during the drive out here from NY the odometer and speedometer stopped working so my mom had to keep track of the speed using the mile markers while my dad drove. While I still have all the guts out, I figured it’s a good time to go through all these wires and try to find the speedometer issue. So I got in there. I decided not to remove the entire dashboard because it is apparently really difficult and most people advise you not to try it, but I followed most of this guide for the process up to the actual dash removal.
I don’t want rust and 50 year old dust flakes to fall into my eyeballs, so safety first! I can stay under there until the heat and my face sweat makes my cool safety goggles fog up, and then I have to wait for them to clear out.
The wiring harness is original, but the radio was replaced probably some time in the 80s so whoever did that (Dad?) made some interesting stylistic choices with their wire connections.
First I took out the glove box and the face vents, then removed the brackets from all the dash lights and gauges and labeled them [mostly]. I bundled the wires from each together and labeled them all.
I feel like I got a pretty good idea of how this thing is wired up just by doing the disassembly part of the exercise. It helped that there are some awesome resources out there on the internet. A site called Advance Auto Wire makes some upgraded wiring harnesses for select classics, but they also did the work of creating color-coded wiring diagrams for free for all the known variations of those classics. There are a bunch of possible versions of the 1972 MGB so I traced the wires of known origin back to their sources and used those to narrow down which diagram I should use as a reference. Frustratingly, there are a few wires of no origin and no destination, so those threw me off for a bit. I didn’t buy a new harness because mine is actually in really good shape, but I love that site so they get a plug.
Again, this car is old as heck and most of its parts are original. So while they were in my hands, I scrubbed the metal parts with a toothbrush and white vinegar, which worked miracles on 50 years worth of rust and grime. I scrubbed the plastic with another brush and some trim cleaner. The clean shiny gauges look so good!
The bezels for all the gauges and lights are chrome but for the switches they are painted plastic, so I got new switches. The blue lens for the high beam indicator has been missing for a long time so I scoured the internet until I could find the right kind of replacement, and got one on eBay. It looks so good, I went back and got a red one too (otherwise the bezel thicknesses are slightly different between new and old and that’ll annoy me). I was really excited about the blue lens though, it was surprisingly hard to find.
Reassembly was much easier than disassembly for the most part. I put all the gauges back in, referred to the wiring diagram and the internet to make sure I was plugging stuff back in the right way, and everything looked great.
The battery was new 5 years ago but has been sitting for a while and was completely dead and about at the end of its life so I bought a new one. I also added a quick disconnect to the negative terminal so I don’t have to worry about draining a lot of power if I’m not going to be driving for a little while.
Much to my complete and utter shock, the car actually started with the new battery! The key hasn’t been turned in the ignition since it was rolled onto a giant flatbed in March 2018 to be shipped down here, so that was a super pleasant surprise.
The original plan was to get the car into good enough running state to bring it to a shop less than a mile away to get the rust holes repaired. I don’t have welding equipment and after trying and failing to learn to weld in college I don’t plan on starting again now. But when I tried to put the gas on, the engine immediately cut out. I remembered I had to empty the tank for storage, so I put a few gallons in from a gas can and tried again. Same results. So my next project will be resolving that.
Short Story
I got a nice replacement radio from RetroSound and obviously need to wire it and its new speakers up before putting the carpet back in. I had my multimeter out and I was probing around trying to figure out which wire provided 12V power when the ignition was on. I could swear it was supposed to be the green wire, all the diagrams say it is the green wire, but for some reason the green one was directly connected to ground. The green wire also already had the right kind of terminal connected to it because it was hooked to the previous radio. But that wire was not only providing no power, it was grounded.
The circuits in the car are relatively isolated from each other and the obvious place to start looking was the stuff I touched most recently, so it wasn’t too difficult to track down. The fuse box has four fuses and thankfully only one of them was blown - the one in the green circuit. The green circuit has three isolated loops; one to the tach and to the dashboard voltage regulator, one to the hazards, and one to the reverse lights. I disconnected the hazards and reverse lights from the fuse box just to make sure I was in the right place and sure enough, immediately blew out the fuse again as soon as I turned the key.
Next step was to start taking out the gauges I had so carefully replaced. When I looked from the back with all the gauges in place, nothing looked wrong. If the short was on the side coming out of the voltage regulator it could be anywhere. I’d have to disassemble the whole thing again to find it. I inspected all the wires and didn’t see anything frayed or torn or disconnected, but did some cleanup just in case. Then I started with the tachometer.
I reached back there and removed the bracket to look at the wires up close and nothing looked off. I was so confused. I disconnected everything again and probed my green wire and lo and behold, no ground connection! Turns out there are two spade terminals on the back of the tach. One of them goes directly to the body, but was previously not connected because the ground wire was attached directly to the bracket holding the tach in the dash. It’s pretty hard to see from the back, especially with the other wires plugged in, so I had plugged power to the easier-to-access terminal, hooking power directly to ground. Now that I look at it again, it’s super obvious that the terminal I had wired up was supposed to be ground, but the power terminal is hard to see from the back when the gauge is installed in the dash, so I’m going to forgive myself that silly error and pat myself on the back for finding it before ripping too many things apart or starting a fire.
