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MG MGB Technical - Ignition light on when ignition off

Upon arriving at work today, my ignition light illuminated once I turned off the car (70 roadster). The car restarted fine, and the light is off while running, but continues illuminated while car off. I checked the archives and saw a response from Paul Hunt on the same thing for a 78 saying there could be power not only to the light, but also the fuel pump (bad!). As I am at work and can't troubleshoot right now, I ran out and disconnected the battery. The archives indicate starting troubleshooting with the voltage regulator, any other thoughts?

Thanks,

Scott
S. M. Chafian

Probably the regulator in the alternator going bad.
Keith Gustafson

Same thing happened to me, and Keith is right,
its a bad regulator in the Alt. Replacing with a spare
alternator solved the problem.
Ronald

Hi Scott.

Most likely a blown diode in the rectifier pack on the alternator.

I was able to locate and disconnect a dead diode on a Delco alternator, soldered in a 40Amp diode I got from a electronics shop.
Not sure about this on a Lucas one though.

Moss list 3 rectifier packs depending on model.

Cheers
Ian F

Ian Fraser

Scott, I had the same thing happen once and after switch alternators it still happened. Sometimes I could slam the door and the light would go off only to come back on a short time later. Two or three times the battery was completely drained the next time I came out to the car.

I just happened to be looking in the engine bay after stopping the car and the light wouldn't go off. I saw a bit of smoke coming from around the starter. I got under there and the wires were filthy and was probably causing connections where there shouldn't be any connections. I took the wires off, cleaned them up, then put them back on properly - no more problems.

Since this is fairly simple to do, I would try this before trying anything with the alternator.

Robert
Robert Rushing

I purchased a B project that was like that. It turned out the PO had put the battery in backwards and blew the alternater diodes. And of course he also got the tach while he was at it. I'm sure though if he had known what he was doing, he probably wouldn't have been selling it.
John

Scott,

Almost certainly the diode stack as others have mentioned. Very easy fix if you can handle a soldering iron, and the rectifier is pretty cheap. Disconnect the battery when you park the car in the meantime.

I've actually had to do this twice, both right after charging a dead battery. Now I disconnect the alternator before charging.

Derek
'79B
Derek Berger

This thread was discussed between 15/04/2003 and 18/04/2003

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