Weird - posted a reply, but it disappeared?

Anyway, I've been driving about and so far the voltage is holding at about 12.5-12.7 volts. Oddly there is not jump in voltage when the truck is running to indicate the alt is charging, but it seems to be holding and maintaining charge.

 

Are you measuring the volts on the battery or the Alternator Battery Post (that goes to the Starter relay)? If the latter, that should be 13.7-14.4 volts - less wouldn't charge your battery.

 

I have been measuring on the battery, but I just went out and checked on the post on the starter relay that goes to the alternator (I think that is what you mean by "alternator battery post"?). Anyway I am getting the same reading there. I have driven a good 50-60 plus miles with probably two dozen or more starts and no run down on the battery, so I must be doing the charge test wrong(?).

 

Put the Multimeter negative on the battery negative post and put the Multimeter positive on the Alternator post (that has the cable running to the starter relay) and you should see 13.7-14.4 volts with the engine running, anything less and you're not charging the battery. Likely the alternator will pass a bench test but still isn't producing enough volts to get the job done.

 

Yea, the battery ran out of juice - it is not charging. The alternator has a lifetime warranty, so back to O'Rielly's for a new alternator.

 

fyi: I went through multiple lifetime Oreilly/Autozone alternators, finally just bought a NEW Alternator online (Jegs/Summit). Been fine ever since (year later).

 

So I got it fixed and the issue was not what I would have expected. After going over everything and replacing some of the wiring and fusible link the issue was fixed by replacing the crumbling plastic instrument panel mounting gauge. Go figure. Running a strong 14v ever since and can finally use my lights lol.

 

Glad you got it fixed! Q: Whats the instrument panel mounting gauge?

 

Yeah, I meant mounting plate - the plastic piece.

 

Did a whole write-up to see if I could help, then noticed the next page and see you got it fixed! Glad to hear.
not sure what a plastic plate in the dash would have had to do with it, but the results are the results. Glad it's working.

On a side note though, what about all the main grounds? Since this is an engine swap (and by a PO to boot!) are all the original grounds that would have been on a '79 still present?
The main cable should go directly to the engine block. Just about anywhere is acceptable, but closer to the starter motor you can get it is a little "better" to my mind.
There should be a ground from the battery to the body too, usually at the fender. I add larger ones and attach them to one of the starter relay bolts, but just about anywhere is good.
And due to the swap, the main reason I brought his all up is that there would have been a braided strap bolted between the back of the intake manifold and the firewall. I think this one is very important and they get removed a lot of times and not put back when engine swaps take place.

So just some other things to think about while you're bringing your truck back to peak condition.

Paul