66 New headlamp harness, position of voltage regulator plug
I am replacing the headlamp harness on my 66 today. When I took put the voltage regulator plug onto the voltage regulator, I noticed that the new harness only utilizes 3 out of the four possible slots that can be wired to the voltage regulator.
My old wiring harness utilized all four slots.
These are my questions:
1.What orientation should I put on the connector to the voltage regulator?- empty slot on top or empty slot on the bottom.
2.Why is the new harness only using 3 of four slots.
3.And, most important, if I put the connector on the regulator the wrong orientation, what could happen?
The new wirning harness for the headlamps and alt are in, no problems whatsoever, thankfully.
What the mish mosh of wires and splices the previous other owners had done, it is a wonder the car ran as well as it did. Between the burnt and melted wiring I am just wishing I had done this last year.
In terms of the 4th wire on the volt regulator plug on the old harness, I know it was on the Field terminal. I traced the wire through the burnt harness, it eventually connected to the ALT wiring harness. No idea if it was doing anything or not, as the P/O had put a fourth wire on the ALT, on an unused terminal that isnt even marked, not the GRD, BAT or FLD, so who knows.
Most likely, this old harness was from another Ford, as the color scheme of the wires at the volt reg connector does not even match up to what the stock should be.
I have it back to what it is supposed to be- things are good!
Hello. The harness that you took off was for a Mustang with a charge indicator light instead of the gauge. The other post on the back of the alternator is the stator post, which should have had a white wire with a black stripe attached to it. That wire goes over to the voltage regulator, and is the mysterious fourth wire.
And, as an addendum, or as Paul Harvey used to say, "now you know the rest of the story", here is what you want to be sure of-
Hook the voltage regulator wire harness plug the proper way to the voltage regulator- learn from me!
I thought, by looking at the manual, that the white wire was on the "top". Well, it "is", but if you orient the picture in the manual to the actual position that the volt regulator is bolted on the car, at least on my car, then the white goes on the BOTTOM.
Or, another easier way to do it, just make sure the white wire goes on the "F" terminal on the regulator(they have lettered markings on them- though my "new" one didnt have the letters).
I drove around for a week thinking everything was fine, until realizing on Thurs night that the headlamps and gauge cluster seemed real dim. Odd.
Put the volt meter on the car when I got home while it was still running, only about 11.5 volts, ALT was not charging the batt- OK- figure lucky I got home, the ALT is burnt out, buy a new one, that is that.
Brought the old ALT to Advance Auto, they tested it, it only charged up to about 11 volts or so on their meter, seemed like a slam dunk, no doubt, the ALT MUST BE THE PROBLEM- right? Nope.
Put the new ALT in this am, started up the car, only 11.5 on the battery, in other words, the bat was not charging from the alt, gee, I must have gotten a bad alt, it happens, right? Nope.
Did a test to check the voltage reg(one month old regulator I might add), running the car, used a jumper wire from + batt to F on the Alt, the voltage did temp jump up to 14, so now I am like, what the heck, the NEW volt regulator must be bad, so I put in my old volt regulator(which was working when I replaced it- never throw working parts away, I only changed it because the case on it was cruddy and ugly).
So, did the same test, the OLD volt regulator was testing as if it was burnt out also.
Took both the new ALT and the new Volt Reg back to Adv Auto. They tested the new ALT, no issue at all, it was properly putting out the correct voltage. I swapped out the new Volt reg for another new one(this "new" one actually did have the Letters on it, which helped me later on).
Came back home, looked at the Volt reg first, the old one was still in. I was noticing that the white wire was not on the F term of the regulator, figured that well, the white wire on the ALT is on the F term, so probably the white wire should be on the F term on the Volt Regulator.
The lighting bolt then hit me, DUH, I have the Volt Reg harness plug on BACKWARDS, so for a week, the car was running off the battery, and maybe, not sure of this, I burnt out my alternator as a result?
Anyway, put the new ALT back in, changed that Volt Regulator plug so the white wire was now on the F term, and sure enough, not only did it start, but the ALT was putting out the expected 14 or so volts.
Just sharing this long winded but happy ending story to try to assist some other poor soul, do let this happen to you!! ha
66 New headlamp harness, position of voltage regulator plug 
The harness that you took off was for a Mustang with a charge indicator light instead of the gauge. The other post on the back of the alternator is the stator post, which should have had a white wire with a black stripe attached to it. That wire goes over to the voltage regulator, and is the mysterious fourth wire. 
