Well, I thought I had it all on right, but as you can see from my other most recent thread, I'm now having my doubts.....

My alternator may not be charging, but I may just have the wires hooked up wrong. What wires are supposed to go from what points on the alternator, to what things in the truck? It is a stock 3 wire unit, and a stock 79 Duraspark distributor and ignition module.

Thanks, AleX

 

Does your dash have an ALT light or an ammeter?

 

If it's just the three wire unit, the top wire is the battery, the middle is the field wire going to the voltage regulator, the bottom is the ground wire, goes to a ground wherever.

 

It has an ammeter, although it's not working....

And it is a 3 wire unit I think, but there are 5 or 6 terminals.

 

The field stud of the alternator should be marked FLD or F, and this goes to the F terminal of the voltage regulator. The stator terminal of the alternator should be marked STA or S. In your setup, this would go to the factory electric choke (if equipped - most aftermarket carbuertors call for 12-volts hot-in-RUN which is different). The S terminal of the voltage regulator is powered by hot-in-RUN from the cab, which I think is GREEN with a RED stripe; although you'd want to check with a wiring diagram.

The large output stud of the alternator should be marked B+ or something similar. This goes to two places - one heavy-gauge wire with a fusible link goes to the battery-side of the solenoid; another wire goes to the A terminal of the voltage regulator. The latter is the sense input to the regulator.

If your alternator has a ground stud (GND), you may connect it to one of the voltage regulator mounting bolts with a ring terminal. This helps keep both the alternator and regulator at the exact same ground potential, in case the two grounds shift over time (due to an aging ground strap, etc).

With your setup, the I terminal of the voltage regulator is not connected.

 

OK, so what I see on mine: The FLD terminal does indeed connect to the F terminal on the regulator. The S terminal at the regulator does connect (via green wire with red stripe) to the wire bundle going into the cab. The wire that I have had connected to the S alternator terminal goes nowhere right now, but yes, used to connect to the stock electric choke. I have my current aftermarket carb electric choke hooked up to the FLD terminal on the alternator, and it seems to be working well.

I have the fusible wire from the fat BAT alternator terminal to the positive side of the solenoid, but I have no other wire going to the voltage regulator A terminal. Could this be why my battery won't charge? I've never touched these wires though, and the truck has held a charge just fine before. I've driven it off and on for 2 years now.

 

Yikes, that's a no-no. Do not hook it up this way. The FLD terminal of the alternator serves as the input to the rotor windings - it gets driven by the field output of the regulator. If you connect a choke there, you'll shift the loading of the regulator and the alternator may not even come online. Furthermore, the regulator is not meant to source that kind of current.

Are you saying that the A terminal of your regulator goes to nothing? If that's the case, it's impossible for the charging system to work.

 

Oh yikes, maybe that's what was preventing my battery from charging..... But my alternator tested bad..... Well I know now either way. Where should I connect the choke then?

And yup, that's what I'm seeing. The A terminal has 2 yellow wires coming out of it, one of which just ends about 2 inches out in a little single plug with nothing plugged into it, and the other one of which snakes down into the main harness. It never comes out, and I can feel that it and several others are just looped around in there. And the 3 wires that do come out are all accounted for.

My charging system has worked though in the past.... I've always thought that the whole thing is set up kind of screwy, my truck's had so many amateur mechanic owners, including me, but it seems like I'm the first one in 30 years that's at least cared.

 

The one wire from the A terminal of the regulator that goes to nothing is probably for the ignition noise suppression capacitor. Leaving that disconnected won't affect the charging system, but you'll want to make sure the connector doesn't short to ground against any sheetmetal. It's un-fused and hot at all times.

The other wire from the A terminal that goes up through the harness is probably where power is coming from. To make sure, disconnect the battery (negative cable first, positive second as always) and test for continuity between the inside of that little plug coming off the A terminal, and the positive battery cable. That will tell you if it ends up being connected, without having to peel back your harness.

Take a quick look at the first diagram in this post, it shows a generic diagram from a Ford shop manual: https://www.ford-trucks.com/forums/9...ml#post9243162

The aftermarket choke should connect to 12-volts hot-in-RUN, and it should be a fused source. My '79 has a 2-connector pigtail hanging from the firewall near the heater box; this used to connect to the stock carburetor. One signal connects to the stator terminal of the alternator, and went to the factory choke. The other is hot-in-RUN and powered the original idle stop solenoid. It's also protected in the fuse panel. I use the latter of the two and I recommend you do the same. I don't remember which color was which, but you can easily check with the engine OFF and the key in RUN and test which one has 12 volts on it.

 

There is a 3 wire plug that sits a few inches from the regulator, and plugs into the main wiring harness that goes back into the cab. There are 2 small gauge wires in it, one red with yellow stripe, one yellow with black stripe, and then one larger gauge wire, black with a double yellow stripe. That came off with the regulator and old alternator harness (I'm doing a 3g swap), and so I'm wondering what it powers?

 

I have Tuff Stuff 3 wire hook up in my 1973 f100, I hooked it up like the diagram said and when I start my truck the truck won't turn off, now when unhook the the 2 wires from the alternator the truck turns on and off just fine, also when everything is hooked up the alternator sounds like its running ruff, like drawing power from something else.