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MG MGB Technical - am i..that stupid

Replacing 12V batteries from my ī68 MGB. I probably switch + and - because my alternator got all hot and smokey and my red dashboard light is on even if i dont have the key in the ignition hole. Can it be that i screwed up the alternator? or did i blew a fuse that i dont now? and what to do now?
Marc Passet

12v Batter*ies*? You should have either 2 6v or 1 12v in the car. Also, the clamps should only fit one way round, IIRC.
dave

Marc;

Not stupid, just going through the learning curve that all of us have experienced.

If you wired up two 12 volt batteries in series, then you made your system a 24 volt system. Pretty much you just killed your alternator. So plan on replacing that for starters. The red light is supposed to be a warning light for a dead alternator, but if it is on without the key in the dash, you may have a short somewhere.

Now, if you wired up the batteries in reverse, then you may have killed just about all of your electrics. Test everything and also test all your wiring. You could have caused a short or shorts by melting wiring and meggering all the wiring is the only way to find out if it is ok.

Think of this as an opportunity to get to know your electrical system up close and personal, a good thing for an MGB.
Ron Kluwe

Unless I'm mistaken, the red light stays on when the battery voltage exceeds the alternator output. If this is correct, then wouldn't the light stay on if there was - in fact - 24 volts coming out of the batteries?
Tony Calleja

Tony. A very interesting question. Perhaps Paul Hunt could enlighten us as I should also like to know the answer.

Marc. If your 68 is original, it has the Lucas 16AC alternator and a seperate, solid state, voltage regulator. At the very least, I would look at replacing both. On my 68GT, I switched to a later model alternator, the Lucas 18ACR with has an internal voltage regulator and is easier to find. There is a lot of information on changing to different alternators in the archives. This may be an opportunity to upgrade to a higher output alternator rather than the somewhat rarer 16AC. Les
Les Bengtson

Thanks everbody,

I didnīt made a 24V system, just used one 12V. System was already converted to 12v. But i probably made a short and reversed the batteries, which in my opinion explains . But Does that also explain the red dash light stay on?

sorry to need your help again
Marc Passet

additional info

What made me confused was that the lights did work with the battery clamps either reversed and normal. also i the starter moter is stil working if i switch the ignition key. Can the work if i blew the alternator?

Marc
Marc Passet

Marc - It sounds very much like you reversed the battery leads and burned out the diode in the alternator. now that you have the polarity straightened out, everything should work ok, except that you will not get a charge until you have replaced the alternator (and the regulator if it is seperate from the alternator). Good luck - Dave
David DuBois

You fried and melted the wires for the alternator. Now that the insulation is melted away and the bare wires are all touching, probably in the harness somewhere near the alternator, the wire for the igniton light is being supplied by the hot feed from battery to alternator (or a situation similar to this- I will wager money on it). DON'T just replace the alternator and try hooking it up without going through all of your wiring to see where it's been melted.

headlights and starter motors don't care about polarity, so they'll work even with a reverse hookup. If you left your battery backward long enough to try the headlights and starter motor, I think you may have done some serious damage to your wiring. Good luck and keep us posted.

Mark
Mark

This thread was discussed between 25/03/2005 and 27/03/2005

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