12v computer?
 

I believe mine is toast. Alt. tests good, fuse is good, wiring is fine(so it looks), so it only leaves the computer. Would one from an auto work on a manual?

What's the truck doing by the way? I only ask because, and I could be wrong here, the computer in these trucks with the 12 valves has a very limited job. For the most part, the most important jobs it does is control the pre-heater in the intake at start-up and the shut off selenoid. Outside of that, the mechanical 12 valve takes care of the rest, or at least that's the impression I've been under. Hopefully someone can confirm this or correct me if I'm way off base.

It also controls the alternator and tach. So I am told.

I would check the crank sensor first. If the tach isnt working.

Look here-linky

It wont charge. the alt tests good, batts are bout 3 mths old, got a new fuse in it, and the wiring looks in good shape
i've been fighting this for a month now lol

oh and the tach and everything else works just no alt charge

Mine started the same thing. Everytime I went to get the alternator checked on the truck it passed. I took it off and took it in and they pulled the brushes and that was the problem.New brushes and they just smoothed out the brass ring they ride on and it was back in the game.

Well i got a diff alt sittin here thats good i'll throw it on to see if it works. If not i dunno, guess throw a comp at it?

It's somewhat common for the voltage regulation section of the 12 valve PCM to fail.
No big deal, charging can be restored with any 12 volt stand alone regulator available at most autoparts for around $15 without effecting other PCM functions.

Remove the two smaller stock wires, tape them to insulate and wire it as below. All modern regulators have the triangular plug. Most important thing is that the switched 12 volt connects to the top connector. The two wires to the alternator can be reversed, it makes no difference.

https://www.dieseltruckresource.com/...egulator21.jpg

Arent these trucks internally regulated?

If you mean internal to the PCM, yes.

I just ask because I dont have that regulator you have pictured. My old 77 gasser does though.

On our trucks, the regulator is in the pcm. What infidel is suggesting is to go with an aftermarket regulator. You can disconnect your alternator from your pcm without ill effects and then hook it up to an external regulator. This is just another option if you don't want to replace your pcm.

At the prices the pcm's are going for i'll take the external regulator...

Thanks Bill!

Yes and after your done with that you can put your tailights and headlights on toggle switches and your starter on a horn button, where does it end.I think i will help you find a PCM i am sure we can dig one up.