Sorry for starting a new thread but I've read all the others and still can't figure out my problem. Can someone see something I don't?

I recently bought a 1974 f250 390 with a 1g alternator not charging. The truck has an ammater which doesn't seem to work (always points up).

The big black wire going to the red terminal on the alternator is connected to the battery and reads 12.8v at all times.

The orange wire going to the white terminal (F) on the back of the alternator is connected to the field terminal on the regulator and reads 11.8v with the key switched on.
Should it have more voltage? The back of the alternator is magnetized, but it is much stronger if I jump the battery terminal to the field terminal.

I am not sure where the wire from the S terminal on the alternator goes.
The wire to the S terminal on the regulator I believe is hot when the key is on.

I have a ground from the back of the alternator to the regulator mounted on the rad support and a ground from the fender to the negative on the battery.

I've already swapped out a new alternator and regulator. Please help me stop unnecessarily changing parts and wasting time. Thanks!

 

 

I believe that is how it is wired.

 

This one shows 4 wires to alt.

 

Are the fusible links good ?

 

The first diagram is for trucks with an ammeter. Like mine.

The second diagram is for truck with a battery light.

As for fusible links, yes my fuses should be good since I am able to read voltage at both the battery terminals and the field terminals.

 

If you have power to the cab and all the accessories (and since you can crank the starter and start the engine, you do), then the main fusible link in the Black wire is still good.

If you pull the connector off of the regulator you should read full battery voltage on the Yellow wire. Measure the battery and if it has 12.8 still and the Yellow wire has only 10, for example, then something is wrong with the wire and needs to be fixed/replaced. It needs to be as close to actual battery voltage as is possible.
You are correct that the Green w/red "S" wire should have 12v with the key in ON only. Not in ACC.
The reading on the Field wire sounds high to me, but I've never made much of a practice of measuring the different ones since they were rarely the fault. However, if you apply 12v to the Orange field wire (called "full-fielding") while the engine is running you should hear the engine idle lower a little bit as the alternator goes all out and your battery voltage reading should go up from 15v to whatever it will peak at. Usually at 17v or maybe even more. But you're only letting it do this for a moment while you check things, so you don't overwork the alternator or damage the battery and other things.
If you have sensitive electronic devices I would not do this test. Instead have it done off the vehicle in a test stand at a store.

Unfortunately you could have received bad new parts too. Not uncommon with the regulators these days. And though maybe not as common, it's not unheard of to get a bum alternator right out of the box too.

But check wires first anyway. It's free and relatively easy with these setups.

Good luck.

Paul

 

Oh, and just for giggles, disconnect that second Yellow wire from the regulator connected to the radio noise suppressor capacitor near the regulator.
Have had them go bad and stop an ignition coil from sparking, but have never had one go bad at the regulator before, so don't really know what it would do.

Paul

 

Another option is pitching that alternator for a gm 1 wire. 12v + wire and done! This also rids you of the voltage regulator🍿