Its actually not puzzling. The factory tach instrument panel has an alternator indicator warning light and the non-tach instrument panel has an ammeter. There are significant differences in the wiring for factory tach vs. non-tach instrument clusters, including the short alternator to regulator wiring harness.
Does the alternator warning light in the instrument panel operate correctly? I will look at my wiring diagram. That 4th wire that is not connected may go to the stator terminal on the alternator to control the warning light in the instrument panel.
I may sound like a broken record, but I suggest purchasing a set of the reprinted factory shop manuals from someplace like National Parts Depot. They are a valuable source of information.
That extra black wire you speak of could be for a small condenser/ charge suppressor. That was usually installed on one of the screws that held the voltage regulator to the shock tower, it was simply to cut down on radio interference from the alternator. Check a diagram to be sure. JTS 71 Mach1
I have tried to attach a pdf file of the alternator wiring diagram. I don't know if it worked. It's my first time attaching pdf files. If it works, look it over. I may have been incorrect on my previous post regarding where it connects.
I don't see the extra wire depicted in either diagram, but they sure had them. If memory serves me right most, but not all Fords had them back then. JTS 71 Mach1
Both diagrams I have are like the pdf diagram I posted. A picture of the actual condition might help. Maybe a PO added it for some reason. The diagram shows a ground wire, but doesn't call out a color. I wonder if its symbolic to indicate both the alternator and regulator share the same chassis ground.
I attached a pic of a new harness which is exactly the same one I have. The black wire is the bottom thin one on the plug with female end. I grounded that wire to the chassis for the time being.
You might be correct in grounding it. Does the other end of it, at the voltage regulator end go to ground as well? That is what is shown in the wiring diagram. Kind of strange they ran an additional ground wire, but that may very well be the case.
All of a sudden my tach works and all i did was plug in the brake warning light plug. I was trying to reset the brake warning light by bleeding the two front brakes (original disc). They reset but then come right back on as i pump my brakes. possible proportional valve?
I don't think it would be the proportioning valve. If the light went out and then came back on, you probably still have some air in the brake lines. I would recommend using a vacuum bleeder. You need to start with the Right rear, (passenger side) then the left rear, right front, and finally the left front. Be sure to keep the master cylinder full, as you bleed the brakes, because if you ever run dry, you will need to repeat the entire process. I have tried to short cut that and it never worked, I had to start completely over. Second thought, If you are working on the old original brakes, may I suggest doing a complete replacement, of the Master cylinder, both front calipers, the rear wheel cylinders, as well as the rubber lines from the body to the rear axle, and the front hoses to the calipers. I also blew the crud out of the steel lines with an air hose. Just be sure there is no moisture, or water in you compressor, or air lines as this is the biggest enemy of a brake system, "moisture". I did this complete replacement on a 1980 Trans Am. It saved me from fighting the bleeders breaking, or rounding off etc. It was the simplest upgrade I could do, and when done it stopped perfectly, well as good as a new Trans Am did in 1980, which wasn't terrible. If the drums and rotors are good , buy a better quality brake pad, don't get some high dollar racing pads, as all they will do is eat your rotors and drums. I did all this to my TA and didn't spend $300.00 dollars. The key here was I went to Orielly's and bought the stuff over the counter. Replacement parts! not "Restoration Parts". I saved about $200.00 plus, just by Not looking on Ebay, (which was stupid expensive on all the parts) or the restoration catalogs. The great part was I had a car that stopped better then new, and I didn't spend a ton of money. I called that a win win. Hope it helps. JTS 71 Mach1
PS I was thinking of why your tach started working, when you plugged in the brake warning light. It could have a common ground between the 2 or while you were messing with things, you wiggled something and restored a bad connection. Just some thoughts. JTS
The only possibility I can think of is you bumped into the wiring to the tach when pumping the break pedal and there is a poor connection. Plus, a poor connection in the tach wiring would explain the occasional hard start condition. Otherwise, the tach starting to operate would be completely coincidental. I cannot think of any way the two are related. The tach is hard wired independent of the instrument panel and printed circuit panel.
Does the brake pedal feel good? Do you see any leaks? Usually either a leak or a bad master cylinder will cause the valve to activate the brake warning light. I would be inclined to follow what jts71 Mach1 mentioned and replace all the hydraulic components in the brake system to be safe. Unless you know for certain their age and condition. You can save a little money and usually get away with rebuild kits for the front brake calipers. Do not rebuild the master cylinder or brake cylinders. And don't buy rebuilt brake or master cylinders.
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