In a message dated 98-07-06 11:42:55 EDT, cattias@cats.ucsc.edu writes:
> Help...Got an unusual (to me, anyway) electrical problem, and could use
> some advice. Have noticed the ignition/charging warning light on my '68
> MGB stays on, even after turning off the ignition switch. Car has a Lucas
> 16AC alternator and external regulator. Disconnected and tested the
> switch, which seems to be doing what it's supposed to.
>
> The only wiring "bodge" I can see as a potential problem are the two wires
> to the F and I terminals of the alternator--they may have been in a single
> plug at one time, but now they have individual connectors on them, and
> could have been connected the wrong way 'round. Don't know if that would
> account for the problem. Can anyone provide a description of which wires
> go to which terminals on a 16 AC?
Chris,
On the alternator, you should have a black wire to the - terminal, brown to
the + , brown/green to the F, and brown/yellow to the I. Reversing the I and F
leads should not cause the light to stay on with the key off. My guess is you
have a bad diode or two in the alternator. Power would then flow from the +
lead, through the diodes in reverse, through the brown/yellow wire, and then
to ground through the coil and the fuel pump.
Disconnect the brown/yellow wire from the alternator and measure the voltage
at the I terminal with the key off. I suspect you will find it to be near 12
volts, indicating a failed diode.
If that is not the problem, then you may have a defective or miswired
regulator. The regulator should be wired as follows:
+ brown/black and brown/yellow
- black
F brown/green
B+ brown
If it is wired correctly, lift the brown/black and the brown yellow wire, with
the key off, and connect them together. The light should go out. If it does,
you have a problem with the regulator, if not, you have a short in your wiring
harness somewhere. Disconnect the two wires from each other. If the light now
goes out, you have 12 volts shorted to the brown/yellow wire. If not, there is
a 12 volt short to the brown/black wire. If it were a 12 volt short to the
other side of the lamp, the white wire, the engine would not shut off when you
turned the key off.
Hope this helps,
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition - slated for a V8 soon
'68 MGBGT---organ donor for the '74
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