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MGB electrical issue
Donuts - 21/4/07 at 12:27 PM

My wife has a 1972 MGB.

it has an electrical fault, The ignition light was staying on when the keyswitch was off. I traced this to the alternator and found a loose wire inside. soldering this back on seemed to solve the problem.

Now however the ignition light comes on with the rev's (higher the revs brighter the lamp). the battery seems still to be charging (14v a 3500rpm).

any thoughts on what could be causing this?

cheers

dunc

nitram38 - 21/4/07 at 02:11 PM

Knackered alternator?

zetec7 - 21/4/07 at 02:33 PM

I'd try a different alternator. It's not as bad as a problem I had to sort out on an MGB...when you parked the car and left it in reverse, opening the door would cause the engine to crank, and the car to reverse away on its own. Turns out there was a short in the backup light switch, which takes its power from the solenoid (as does the intereior light). When you opened the door, the circuit was complete to the solenoid, engaging the starter. But only in reverse.

britishtrident - 21/4/07 at 06:58 PM

quote:
Originally posted by Donuts
My wife has a 1972 MGB.

it has an electrical fault, The ignition light was staying on when the keyswitch was off. I traced this to the alternator and found a loose wire inside. soldering this back on seemed to solve the problem.

Now however the ignition light comes on with the rev's (higher the revs brighter the lamp). the battery seems still to be charging (14v a 3500rpm).

any thoughts on what could be causing this?

cheers

dunc


Remove the rear plastic cover from the alternator clean the spade connectors, check the condition of the 3 pin connector -- renew if require.
Check the condition of the main feed from the alternator where it connects to the large lucar spade on battery side of the starter.

If none of the above Alternator regulator is knacker ---

Macbeast - 21/4/07 at 10:00 PM

Sounds like (one of) the diodes is short-circuit. Can't imagine what your loose wire might be doing and I hope you put it back in the right place. However, it's possible that you're putting AC into the battery, which may not do it a lot of good.

I would get auto electrician to give it the once-over.