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MG MGB Technical - '63 Electrical Troubles

Hello All,

The '63 MGB arrived yesterday. What a great car, plenty of power (relative to the T-series), and the overdrive is so nice to have.

But, some bugs. The car sat for 6 years with little use. Over the past year, though, some work was done, including a new generator, battery, and battery cables. Now the ignition warning light stays on, and the headlights, panel lights, map light, and heater motor don't come on when switched. The turn signals and wipers work.

I suspect there is a lot of corrosion, but I haven't had a chance to do any further work. Checked the fuses (the two 35 amp fuses), and they are OK.

Is it possible that there is a single cause for all of these things - like a bad ground or something? Or should I just get the wiring diagram and ohm meter and get to work?

Thanks a lot.
Greg

Greg Van Hook

Greg - The very first thing you need to do it to go to Advance Auto Wire http://www.advanceautowire.com/ click on Stock Schematics and print out the full color wiring diagram for you MGB (better yet, copy the file on a memory stick, take it to Kinko's and have them print a full size copy {14 X 17}of the diagram and then laminate it). Next, check the output of the generator (disconnect the wires going to the generator, jump the two generator terminals together, connect an analog meter set to read 50 volts, start the engine but don't rev it up, slowly increase the revs while watching the meter. You should be able to get the output of the generator to go up to 20 volts at around 1000 - 1500 RPM. If you do, the generator is good, if not you have a bad generator [contact me is this is the case, I have a bunch of generators laying around]. Don't allow the generator to go above 25 volts output while doing this check). If the generator check good, you may have a bad regulator (send it to Bob Jeffers to convert to solid state). From there, you will need to start chasing wires and connections. The bullet connectors are notoriously troublesome and the sleeves should be replaced and the bullets cleaned. Same thing with the ground connections. For a more detailed description of proper connection preparation, see the article, Electrical Connection Preparation in the Other Tech Articles on my web site at: http://homepages.donobi.net/sufuelpumps/ Cheers - Dave
David DuBois

Dave,

You're awesome as always. I really appreciate your help.

Greg
Greg Van Hook

Unlikely to be a common cause. Lights are powered off the brown circuit, the map and panel lights are powered from the main lighting switch in the first position, headlights in the second. If none of the lights are working i.e. parking and number plate lights aren't either then I would suspect a common cause for those three. If the parking lights work then the headlights will be something else, like the dip-switch or the wiring to it from the main lighting switch (blue) or from it towards the front of the car (blue/white and blue/red). The bullets by the right headlight are a common cause. Again if the parking lights work but the map and panels don't then these have their own switch/dimmer rheostat fed from the red.

Heater fan works off the green circuit (fused ignition), but so does the fuel gauge, brake lights, reversing lights and indicators so if these work it is going to be closer to the heater fan switch and the motor and their connections.

First thing for charging is as Dave says - check the dynamo itself, after that it gets a lot more complex to determine just what is wrong.
Paul Hunt

I thought I was on to something about a common cause. Then after I downloaded the diagram that Dave mentioned, it was easy to see I was wrong. Everything on the green circuit works, except the heater fan, while nothing works on the brown side, except the starter. Ugh. I was hoping the word "complex" wouldn't creep into this.....
Greg Van Hook

No time yet to really make much progress on the electrics, but just out playing with the car last night, the heater fan came on after I fiddled with the switch for awhile. Just some corrosion, I guess.

So, everything on the green side works, and nothing on the brown side works. Since the brown side goes through the voltage regulator, and the ignition warning light stays on, I'm beginning to suspect the VR is bad.

Does anyone out the know where I can get a decent used heater fan switch? Mine is broken and I don't want a new one 'cause it won't match the others.

And, is the front turn signal amber or clear? I have one of each!

Thanks,
Greg
Greg Van Hook

The VR itself won't be the cause of the headlights, map or panel lights not working.

Power comes from the solenoid to the VR, then is daisy-chained off there to the ignition, and teed off the VR to the fusebox and the main lighting switch. If the car starts and runs power must be getting to the ignition switch, and if the horn works power must be getting to the fusebox. However if the horn and none of the lights work the tee onto the brown at the VR could be dislodged.
Paul Hunt

Paul,

Yeah, the car starts and runs (with the charging light staying lit), and the horn and none of the lights work. That would be the brown wire going from terminal "B" to the fuse block, right? It's connected, but I haven't looked at that particular the connection for corrosion. Terminal "E" where the black ground wire connected was really rusty.

Thanks a lot,
Greg
Greg Van Hook

The front turn signals were originally clear. To my knowledge, they are NLA so you will have to find another used clear unit or purchase an amber one. RAY
RAY

Ray,

Oops, I wasn't very clear with my tun signal question.

Both front lenses have a clear side and an amber side. On one side the amber flashes, and on the other side, the clear flashes. So, it's just hooked up wrong on one side.

Greg
Greg Van Hook

Greg

I have some fan switches. Pull yours and check it with a conductivity meter. If not good, drop me an e-mail and I will send one out.

I also have a couple of VR's but don't know if they are any good. Came in the parts with my 67.
Bruce-C

This thread was discussed between 23/03/2009 and 26/03/2009

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