Steve -
I'm going to assume that you mean a 11.8v potential between Positive and
Ground. A 1977 MGB is Negative Ground, so the voltage potential between
negative and ground should be zero.
If one of the diodes in the "diode pack" or the protection diode goes
bad, the alternator would have a short to ground, but would still make
power when the car was running. The diodes are available seperately, so
if you're a little adventurous, you can replace just shose parts, rather
than getting a rebuilt alternator.
Chris Kotting
ckotting@iwaynet.net
> Date: Tue, 2 May 2000 02:46:57 EDT
> From: Speedo79@aol.com
> Subject: Alternator Woes
>
> Listers,
>
> I have a draw on the battery in my 1977 MGB due to a short. After I
> disconnect the clock, the potential difference between the battery negative
> and ground is about 11.8v. I start checking the items on the brown (hot) and
> purple (fused hot) circuits, but everything makes the voltmeter jump up to
> ~12.8v (battery voltage). I pull my pullout stereo out, and the potential
> difference drops to about 8.5 volts (I think this is because the stereo has a
> battery that keeps the presets saved. The battery is probably about 3v-does
> this sound right?)
>
> 8.5 volts is still a pretty big draw, so I keep digging around. I start
> pulling wires, when I get to the alternator plug the potential difference
> drops to about 0.5v.
>
> How can my alternator be drawing 8v? Is my alternator bad? Even if it is
> still charging the battery at 13+v? Is there any thing else I should check
> before I take the alternator in for an exchange (Lucas rebuilt alternator,
> lifetime warranty!)?
>
> Thanks for all your suggestions.
>
> Sincerely,
> Steve Sanchez
> 1977 MGB
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