Hey guys,

Hoping to get some input on a charging issue I've been having on the 77' I recently purchased. The last owner installed what looks to be a new re manufactured 60A alternator and voltage regulator. The other day my battery died. I figured it may have been from sitting, since it's been getting cold and this isn't a new battery. After charging it I threw it back in the truck, started the truck and took a quick voltage reading to verify my alternator was charging. I was surprised to read roughly 15.5VDC, which indicated to me that my voltage regulator wasn't doing it's job completely. I swapped in a new unit that I had sitting on the shelf and now I'm reading nearly 18VDC. I'm not ruling out that I have two new and bad voltage regulators but it seems unlikely. I decided to do a deeper dive and make sure the alternator wiring harness wasn't compromised and everything was plugged in where it was supposed to. I pulled the harness, removed the tape, checked the wires, and re-installed. When I went to hook up my alternator again I started questioning something. There are three wires connected to the back of the alternator:

1) Heavier gauge black/red that goes from the red ring terminal on the alternator to the line side of the starter solenoid (battery +).
2) Smaller gauge red wire that goes from the white ring terminal on the alternator to the voltage regulator.
3) Smaller gauge white.black wire that goes from the black ring terminal on the alternator to I believe the choke? Not sure where exactly but according to the schematics this is where it ends up.

Can anyone confirm my wiring? Also, I did forget to check continuity from the alternator to ground. Is is correct to run a designated ground wire to the alternator case?

Thanks!

 

In case you want to replace the alternator wiring harness, that's the one that goes from the alternator to the regulator.
Harness, alternator wiring
Fits 78 F100-350 w/ amp and oil press gauges. All engines and 70 amp Ford alternator
D8TZ-14305-B
Green Sales, Cincinnati, OH (800) 543-4959

Some more help from FTE folks.​
The GREEN with RED stripe wire coming from the cab connects to the 'I' input of the regulator. Note that if this truck was originally wired for gauges, the GREEN with RED stripe wire is sourced differently. If that's the case, you should make that clear.

The STA stud on the back of the alternator connects to the 'S' input of the regulator. If you have a factory electric-assist choke, the STA stud also branches to that.

The 'F' output of the regulator connects directly to the FLD stud on the back of the alternator.

The large output terminal of the alternator (sometimes labeled BATT or B+) connects to the battery side of the starter solenoid through a fusible link as well as the 'A' input of the regulator.

 

I think your alternator isn't recitfing correctly. Probalby getting some AC ripple that's bad for a lot of things.

 

I'd take the alternator off and have it tested ... for free even .... at Advance, AutoZone, etc ... even NAPA .

Those old style tall mechanical regulators ... if you still have one ... can be replaced with newer, electronic regulators. I think was a '86 Echlin one I swapped to in 1986.

 

As you will hear a lot around here, "new does not mean good" anymore.
As was suggested, just have it tested and find out. Of course, there are some tests you can do as well, but you already know it's capable of charging because it has been. Just not the normal levels.

Maybe not, but it's not far out of line of the usual 14.5v you get typically. Borderline worrisome, but not horrible.

Sorry, but not unlikely at all! In fact it's more common to get two, three, or even four or more bad parts in a row. Especially from the same source and same brand.
Sometimes even with another brand you get a bad one.

Correct. Some years it's Black w/yellow, but it sounds like yours is correct.
Were there other wires spliced directly to this Black wire? Does your instrument cluster have an ammeter, or just a battery charge lamp?

Colors aside, what letters are cast into the alternator case adjacent to these terminals? This one should read "FLD" for field. Normally an Orange wire, but sometimes red and sometimes the colors have faded/changed with age.
This FLD wire should run directly to the F terminal of the regulator.

Correct. Should be an "STA" for stator cast into the housing adjacent to this wire terminal location. With an ammeter the only function of this wire is to power the choke on the carburetor. With a battery charge indicator lamp on the dash, it also runs directly to the "S" terminal of the voltage regulator.

It's actually not a bad practice, but from the factory they ground through their case directly to the engine block/cylinder head. Over the years with new paint and new rust, it's not a bad practice to add another one and to be sure that your engine block is well grounded.
Of course, if the starter spins easily and fast, then the block is pretty well grounded.

However there is ALWAYS a dedicated ground between the alternator and the regulator. This is usually a smaller (18 gauge maybe?) Black wire mounted to one of the "GRD" studs on the alternator case and runs up to one of the mounting bolts on the voltage regulator.
This is also assuming that there is a dedicated body ground wire from the battery to the body somewhere nearby.

A helpful hint is to NEVER attach the regulator to battery power before it's mounted to the body with this ground wire. You can fry a regulator pretty easily if the battery is connected before the regulator is grounded.
Verify you have a ground between the regulator and the alternator. Then see if someone can test the regulators you have and maybe get a third.
I hate to spend your money by throwing more at the regulators, but it's a fact that so many of them are bad right out of the box anymore that you can't just assume they're good.

Good luck.

Paul