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ALtenator brown wire

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S

Southbound

Freshman Member
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I hope someone can help...I have a 75 tr6 and have a question about the wires running to the altenator. There is a small wire it's brown coming from the altenator. I think is for the ignition warning light but when I disconnect it from the altenator I get 12 volts with my meter when I attach it to the disconnected wire.
Whats up with that? When I leave it connected the ignition lite stays lit even with the keys out and off.
I appriciate your help
 
The small brown wire is supposed to be hot all the time. It's used so the voltage regulator inside the alternator can 'see' the battery voltage, without being fooled by the voltage drop in the large brown wire.

The wire to the light is brown with a yellow tracer on it.

Most likely, the regulator inside the alternator has failed, which is why your light stays on. Since the small brown wire powers the regulator, disconnecting it will make the light go out, but it will also disable the alternator.
 
Thanks for the reply...On the amp meter in the car it shows its charging when the car is running even though the wire is unpluged. Is that possible?
 
Did you install an ammeter?? In '72, they started using voltmeters not ammeters.
 
Some alternators will charge with the small brown wire disconnected (some will also overcharge). But if the red light is on, it's very unlikely it's actually charging.

Or miswiring might be a possibility? I think by 75 you should have just a 3-terminal "Euro" plug and a single quickconnect for the small brown wire so no way to get them confused. But if someone has adapted an earlier (or different) alternator ...

And as Art says, a 75 would not have an ammeter, unless someone has added it. The voltmeters were so inaccurate that I wouldn't put a lot of faith in it, unless you've checked it against a digital or moving coil voltmeter.
 
sorry my bad voltmeter.I had some beer when I was posting. The car is all original stock so I guess the regulator inside is the culprit. It's funny that the light goes out once the car starts but when the cars turned off the light comes on. Thats what I still dont understand. The "voltmeter" reads fine.
hmmm
 
With the ignition key in the "off" position see if you have 12 volts at the white wire on the fuse box. I believe you will have a white wire on one side of the fuse and green on the other side of the fuse. There shouldn't be voltage there until the ignition key is in the "on" position.
 
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