[Durango_Boy]

I have a 1978 Dodge D100 truck, a 2x4, that came stock with a slant 6 and a 4 spd manual OD transmission.

I replaced the drive train with a 360 from a 1997 Jeep grand Cherokee and a TH727.

The harness basically traded perfectly onto the '97 360 despite being 20 years different.

Question, does the 1997 Jeep Grand Cherokee use an external voltage regulator like the old dodge does, or is it's alternator internally regulated?

I ask because the truck used to run great. They the battery went dead on me despite having an alternator seemingly putting out just fine after being replaced. The battery tested fine, yet when the engine is running with a full charge I can watch with a meter the voltage dropping a tenth at a time.

I next suspected the external voltage regulator, that was replaced about 5 years ago. I'll replace it and see if that fixes the problem but I'm wondering if the new engine with modern alternator is internally regulated or not, or if it's external and I just have a bad part to deal with.

Thanks.

[enkeivette]

I'm almost positive that alternator would be internally regulated. Ditch the external regulator, see if the voltage jumps back up. Have you tried putting a multi-meter right on the alt while it's spinning? That should answer your question right there.

And make sure there's a belt on the alternator.

[Durango_Boy]

Originally Posted by enkeivette

I'm almost positive that alternator would be internally regulated. Ditch the external regulator, see if the voltage jumps back up. Have you tried putting a multi-meter right on the alt while it's spinning? That should answer your question right there.

And make sure there's a belt on the alternator.

The setup is all serpentine so the belt is constantly tight and well adjusted.

I'm skeptical about the regulator being internal simply because it's wired to the harness just like the old style alt. There is a heavy gauge power wire that goes to the battery...a ground to the bracket, and a pair of green field wires that don't need to be a certain way. I put the meter on the alternator with it running and the voltage was dropping a tenth at a time just like the battery and it certainly wasn't 13V+ like it should be. It was under 12.5V and falling. That's why I know it's not charging. However, I took the new alternator back off, had it tested by the professional rebuilder and he said it checked out. I also then had the battery tested and charged and it passed.

I'm going to go ahead and replace the voltage regulator and see if that makes the difference. Like I said, this combination all worked great for a few years and now all of a sudden there are problems.

[enkeivette]

I had this exact same problem on a Camaro, IROC. Voltage measured 12.5... 12.4... 12.3... every second it would drop, until the motor died. We replaced the alternator, then the battery. Problem was the fuse for the (external voltage regulator?) was missing. Replaced it and everything was copacetic.

Maybe it does need an external regulator.