MGB & GT Forum

Hello
I have had a continuing issue in my recently acquired 1964 MGB with new generator with my new battery discharging within 3 days of being fully charged but not driven. This applied to a recently disposed battery as well as a brand new one. Just tried a test by disconnecting the after-market voltmeter. This made no difference. Any suggestions, please?

banjo33, Sunshine Coast, Australia

Check trunk light staying on. Install a battery disconnect switch.

I don't think 64s had a trunk (boot) light. I can't think of anything that could discharge the battery, if the wiring is standard. A battery cutoff switch is a good idea, but in this case just a bandaid over the problem.

A thought is that maybe the problem is in the battery voltage regulator, it should disconnect the battery when the generator isn't generating. Maybe that is stuck, see Lucas booklet, attached.

Herb

Are you sure that the new generator is actually charging the battery? What is the charge state of the battery when you park it after a run?

Did you polarize the generator?

"Polarizing the generator is something that should be done any time a new generator is installed, just as a precaution. fortunately it is very easy to do. After bolting the generator in place and before connecting any of the wires to it, attach a length of wire to the smaller of the two terminals (Field terminal). Touch the other end of the wire to any terminal with voltage on it, preferably the terminal of the starter solenoid where the battery cable connects). Just quickly wipe the end of the wire across the terminal - you should see some small sparks when you do this. Remove the wire from the field terminal of the generator and connect the two wires from the harness to the appropriate terminals and you are done. "


Testing the generator:

http://homepages.donobi.net/sufuelpumps/Other_Subjects/Electrical/General/Generator_Test.pdf


Testing the control box (regulator):

http://www.mgb-stuff.org.uk/controlbox.htm

Really, only the lights and horn are on that circuit.

Might be the main light switch. Originals lasted forever. Replacements do not.

With an amp meter discovering which is not hard.

A cutoff switch works fine but, it is sort of a shade tree mechanic thing.

---

L.W.(Larry)Baygents
63B
77 Spit

When the car is cold reach in and feel the generator. If it's warm then disconnect it and let the car sit overnight. If the problem goes away then you might have a problem with the new generator.

Thanks for your reply, Wray.
It now seems to be that the solenoid may be the culprit.
I will advise after the weekend.

Ian