78 F250 400ci

I’ve searched for the last 2 hours trying to figure out what I have going on but can’t come up with anything. My old alternator went out so I purchased a 100 amp unit from Summit that’s a single wire alternator. Obviously it’s internally regulated so I need to bypass my regulator.

Old wiring is as follows:

2 yellow wires to the A terminal on the voltage regulator
1 white wire to the S terminal on the voltage regulator
1 black wire to the F terminal on the voltage regulator

On the back of the old alternator was a heavy (8 gauge wire) connected to the BAT terminal on the back of the alternator in-line fused to the positive of the starter solenoid.

A ground of course.

And a wire from the FLD terminal on the alternator to the F terminal on the voltage regulator.

I’ve connected an 8ga wire from the post on the new alternator to the starter solenoid and a ground from the alternator to engine block.

Now the truck wont even start. Note: I used all new wiring and completely ditched any factory wiring when hooking up the new alternator. Am I missing something?

 

Far as I remember something does go through the alt wiring, something to do with the key being in the on position after starting, that allows truck to charge while running, and also allows that red/blue starting wire for the solenoid to connect. If you have the alt gauge in the dash then the alt wiring has an important wire. Sorry not more help, been a while since I had to deal with it. Other members will be along shortly I'm sure.

 

That’s what I figured but I feel like some of my wiring isn’t factory so I’m not quite sure.

 

I can't recall the wire color, but there is a wire that supplies the ignition switch from the battery that many people here have forgotten to hook-up after they went the 3G alternator route. Try looking up those threads. For some reason, I recall the wire being yellow with a stripe on it, but don't hold me to that. Also, did you remove the old regulator harness or just unplug it? Finally, I too have a Summit 100A 1 wire unit. I love it. I will say that if you get a battery that has top AND side posts, you can run your alt wire directly to the battery using a superior connector, leaving room for the other wires at the solenoid.

 

Thanks for that info. I’ll have to do some looking at the 3G alternator threads.

I just unplugged the old harness. I was hoping to just be able to jump a couple of terminal on the harness but that didn’t work.

Eventually I will get a battery with top and side posts. This will work for now.

 

Hello.. You need to send power into the truck for key etc I think it is a black/yellow wire not sure. I will look for a pic

 

Hope this helps

 

If you look at the charge wire you removed you will see where it is tied into another wire to feed the ignition. Cut this wire and either add it to the batt side of the solenoid or batt post on the back of the alt.

 

I just found the same image you posted. Thanks so much. That should get me back on the road. I’ll try this after work.