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Discussion Starter · #1 ·
Hi all. I wonder if anyone can help. I have searched high and low for the answer on the web but can't find what I need so hopefully one of you knowledgeable guys can assist!

I swapped out my old Motorcraft 3 wire alternator for a 100 amp Powermaster 1 wire. Install was easy enough but if I just disregard the old harness, the car wont start (I.e. is completely dead). I have to connect a black wire (which seems to come from the wiring harness) to a yellow wire which then goes to the + side of the starter solenoid. Then the car runs fine. It does sometimes struggle under load though - I wonder if the old voltage regulator is still interfering somewhere?

Pics attached - any pointers most welcome!

The car is a '66 Fastback, stock 289 V8.

Thanks a million,

Louis
 

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You need to remove the regulator and the associated old alternator harness. There will be some cut and splicing involved, you’ll need a wiring diagram. If you have an amp gauge in the dash I’d suggest bypassing it as I don’t think it’s up to the task of a high output alternator. ( I may be wrong about that others that have done the swap can chime in). Doesn’t powermaster have an install sheet or something similar on their website?
 

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I think that this might help...
 

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Your 1 wire alternator has a built in voltage regulator. External regulator not needed.
That 1 wire, essentially connects to the + side of the battery.
If your gauge cluster includes a amp meter, that amp meter will be completely useless.
But that’s ok because a good voltmeter is much more useful.
 

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1 wire alternators do not charge as well at low RPMs as a 3-wire. They can't maintain voltage at the bus very well, and they tend to cause battery failures by making the battery charge too fast.

In almost every measurable way, the 1 wire alternators are worse than the 3 wires, and cause more problems than they usually solve.
 
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Discussion Starter · #6 ·
Thanks so much guys. I think I'll put a ground in from the alternator and see if that sorts out the occasional issues with (electric) power and will also try a voltage drop test. Re the mystery wire, I'll do some more digging there. Don't really fancy pulling the loom apart but I may have no choice!
 

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I installed the same one wire alternator you have listed a couple months ago and did not remove the external volt regulator and have no issues that I'm aware of
It seems a lot of times these old cars have been hacked and messed with so much through the years that one person's situation doesn't compare to anothers...
 
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