I had the same experience with a replacement alternator on my 'B. The small
brown wire on the original alternator was probably a voltage sense line for
the regulator. The heavy brown wire, as big as it is, still has some voltage
drop when the alternator is providing charging current. The regulator
(inside the alternator) will adjust the output of the alternator to make the
sense line 14 volts. The point at which the sense line connects to the big
brown wire is the point where the voltage is going to be exactly 14 volts.
Ideally the small brown wire would go all the way back to the battery. Lucas
probably tied the small brown to the big brown wire inside the alternator as
a cost saving measure.
Bob Donahue (Still stuck in the '50s)
Email - bobmgtd@home.com
52 MGTD - NEMGTR #11470
71 MGB - NAMGBR #7-3336
.
----- Original Message -----
From: <MGTD2@aol.com>
To: <mg-t@autox.team.net>
Sent: Wednesday, August 29, 2001 4:16 PM
Subject: MGB alternator (Sorry!)
> I know someone out there can explain this in no time, so let me ask this
question to you, my square-rigged comrades:
>
> My '69 B-GT has a Lucas alternator with three wire attachment via modular
plug.
> 1. Heavy brown (to the battery via starter solenoid)
> 2. Not so heavy brown (diagram shows it also runs to the solenoid)
> 3. Brown w/ yellow to the alternator light.
>
> Question: I bought a rebuilt alternator (came from AutoZone but seems to
have been re-manufactured in the UK) and it only has a 2-wire modular plug.
The size of the terminals makes it appear to be for the two brown leads.
What did I get? What from England uses a 2-wire alternator?
>
> Question two: A little education please-- smaller brown wire performs
what function? Could the 2-wire alternator need only the heavy brown lead
and the brown/yellow lead? Is the smaller gauge brown lead an "exciter"
that stimulates the alternator?
>
> Inquiring minds need to know!
>
> Thanks in advance.
>
> --John Deikis
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