KB83

Hey all, new to the forum. I'm having an issue with a truck I'm working on. I searched the forums and didn't see anything that looked like my problem, so I'm looking to you guys. Some background on the truck... none. A friend of mine hadn't drove the truck in a year because it had a charging issue and she doesn't know anything about it. At all. So we towed it to my house and now I'm trying to go through it from scratch. I don't know much about these trucks and I don't know anything about the history of this truck.

Here's my issue. The battery was dying because the alternator isn't charging. The truck has a brand new battery and a brand new alternator. I'm only getting 12.5 volts at the post on the back of the alternator. I took the alternator to autozone and it passed the test. I have a pretty long list of projects to complete, but I want to get the first known issue (charging) resolved before I move on.

Do you guys have any ideas why the output at the alternator would only be 12.5V but the alternator would be considered good at autozone? FWIW, I'm checking it at about 2k rpms because that's just where its running right now. Its kind of a basket case and I'm hoping to get it all sorted out, but this low voltage issue is bugging me right now. It's running terrible, smokes like crazy, and smells like death but I'm the only one with a garage so it gets to be my headache.

I appreciate any help you guys can offer.

RAD4Runner

Do u have built-in voltage tegulator or external?
Check for 12V at IG terminal of regulator. Or post picture of reg with wire colors.

KB83

I'm pretty sure it's an aftermarket external one. It's mounted to the drivers fender but it looks brand new. The alternator had 3 posts on the back. One case ground, one with a little black thing connected to it, and one without anything connected to it. The voltage at both posts it 12.5V and there is a three wire connector on the back of the alternator. The output is the same with and without the connector hooked up.

WolfMann

Sounds like the voltage regulator, try tapping it with a wench. Also there's two different sets of alternator/regulator for these trucks. A circuit and B circuit, it has to do with the number of pins in the connector and the amps they put out. Make sure you have the right ones.

KB83

Would it make a difference if the regulator wasn’t hooked up? I don’t know enough about these systems, but it seems like the alternator should still have some kind of output even if the regulator weren’t connected. The output was the same with and without the connector hooked up.

Also, which terminal is the IG terminal on the regulator? And is that with the truck running or not when I check for 12V?

thanks for the replies guys. Hopefully y’all can get me straightened out.

RAD4Runner

​​​A picture paints a thousand words.
Let us see what you have in front of you.

Difficult to tell or guess without seeing the regulator and/or schematic. If you do not know whether you have a stock regulator or not, OR if you do not have a schematic, you would have to do your homework of tracing those wires from regulator to battery or to ignition switch, or to the fuses.

There should be these wires going to regulator:
IG- from ignition switch (IG on) - this provides excitation (i.e., seeding the alternator). Red in 1986 and later.
S- Sense wire. usually white. goes directly from battery (or fuse that's always on) to regulator. Always has exactly same voltage as battery.
L - Fault aka "charge fault" wire. yellow in 1986 and later. When IG is on, this is low. When good alternator starts working this goes to 12V.

KB83

I found a manual for it so I’m looking through it now trying to chase this down. What does IC mean in regards to the regulator?

WolfMann

I've heard of people running a wire straight from alt to bat and getting around the regulator like that. But then I suppose you run the risk of an overcharge. That regulator looks almost new, also seems to be a 40amp 5 pin connector, I think that's A circuit. Check the three letters at the port on back of alternator, they'll be different depending on what type it is. If you have a B Circuit alt on an A circuit regulator it won't charge right.

KB83

You are correct, it is s brand new 5 wire regulator. It’s a duralast VR765. I know that because I found the box in the cab with the old one in it. The more I look into this the more it appears to be a diy hack job with a shoddy audio install and everything. The charge light doesn’t look to be working either.

How would I know if it’s an A circuit or B circuit?

WolfMann

5 pin connector, and there should be three letters where 5pin connector plugs into alt. (Back of alternator) I would check those first and make sure you've got the right alt. I can try to take a look at mine sometime tomorrow (dark now) It's also 5 pin a circuit. But a Google search may tell you sooner.

WolfMann

I may have been wrong before, I think A circuit is the 55 amp, 5 pin, system used on 4x4 trucks for this time period, alternator should say FEN on back. The B circuit is 40 amp system (LEF on back) used on 2 wheel drive systems from same time period. Seems to be a lot of confusion on the two systems wherever you look.

WolfMann

The 55 amp system uses an ic regulator (like the one you have) while the 40 amp systems used a mechanical regulator (much bulkier with adjustable tabs inside). I would make sure you have the right alt for your system.

KB83

Ok. I’ll have to look at it later. I drove it back to the friends house so the wife could park her car in the garage again. Apparently she doesn’t like getting into a 30 degree car. Who knew? I have a buddy that had the same exact truck with the same exact problem and he claimed that he didn’t get it resolved until he bought a Toyota regulator. So I looked on eBay and found one for $25. I’ll give that a shot and if it doesn’t work then I guess I’ll have to start going through the wiring. I’m 95% sure it said FEN on the back of the alt.

Thommo Thompson

did this chick ever own it while it was working? (ie it just stopped working for her) or did she unknowingly buy it in its broken state? im trying to ascertain what we know about the history.
if the former, did she habe the work done to have the new regulator installed?? or is that your work, trying to fix the problem?