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MG MGB Technical - Ignition light stays on!?

After completing an oil change on my wife's 1968 Mini, I walked back past the MGB (1967 roadster) in the garage to notice the red ignition light on despite the ignition being switched off. Nothing was left on in the 2 days it had sat in the garage but the batteries (2 six volts) were drained. There was enough power to switch the lights on, heater or wipers but not enough to start the car - just a very slow turn. If you turn the ignition switch to the first click (so the electronic fuel pump starts ticking), then the light goes off instead of coming on as it would usually. Have tried charging the batteries after topping up the electrolyte (one was very low) but the first one I have tried only seems to accept about 1.5 amps of charge before going no further. Am going to try jump starting the car tonight but would welcome any suggestions as to what could be wrong. Does it sound like the alternator? (converted from a Dynamo some time in the past) or could it be the starter solenoid?
Thanks in advance.
Martin Port

How dare you work on a Mini. The MG is in the huff.

Pull the plug out of the back of the alternator and the light should go out. The alternator is faulty so get a replacement from LS (Lucas)Uk local depot. It's only about £25.
Iain MacKintosh

Pulled all of the wires to the alternator and the light stays on. Very confused now. Charged up the batteries and the car starts fine and runs ok. Batteries then discharge overnight if left connected. Any more ideas? Now at the end of my tether!
Martin Port

Martin,

Hi there - for the light to stay on with the plug disconnected from the alt, there must be a short to earth or a load on the thin brown/yellow wire from the alt to the warning light, check carefully.

During the "conversion" from dynamo to alt, was the control box completely taken out of the circuit or is it a bodge using the control box as a terminal block? If so, sort it out! Could be that there is a load generated in the control unit.
Chris at Octarine Services

Hi Chris - only just read your thread which is a shame because it could have saved some time at lunch today! Ended up cutting into the loom to trace the brown/yellow wire from the ignition light - eventually revealed that during the conversion from dynamo to alternator, the previous owner/garage had joined the yellow/brown to a red/green wire which then runs to the alternator. Problem was, they had just twisted the wires together and bound it up with electrician's tape. Bodge of the highest order! As soon as we found it, it started smoking which would explain the battery drain. Going to leave the B at work tonight and spend tomorrow lunchtime putting proper joints in which should hopefully cure the problem. Fingers crossed!
Thanks for your reply though - at least our findings are concurrent with your theory and we found it before the car caught fire!
Regards
Martin Port

This thread was discussed between 31/01/2005 and 03/02/2005

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