Hi everyone!
Would appreciate some help with a possible alternator problem on my 1990 4ZE1 troop. Here are symptoms - first symptom showed up several weeks ago and continued intermittently. It consisted of several dash lights (check engine, e-brake, fuel, etc....) coming on, usually when RPM's were very low. Sometimes they stayed on till engine was shut off, other times they would quickly go out again. After a couple weeks of this, my fan (for AC) began to operate intermittently....ie when the switch was in the on position it would sometimes blow, and other times not blow, sometimes kicking in and out several times a minute. A couple days after the fan problem showed up I went out to start the engine. It started and ran for 2-3 seconds and then shut off. It will do this repeatedly, as many times as I try to start it.

So, after doing some archive searches I am thinking this is most likely the alternator....do others agree? I saw a post that said I could disconnect the main engine relay and see if the motor would continue to run...is this an appropriate method to determine if the alternator is bad? If so can someone clue me in on where the main engine relay is?? Thanks for any help/advice you can give!! It is very much appreciated! <img src="/forums/images/graemlins/cheers.gif" alt="" />

I would definitely say there's a good chance of it based on the information provided. Of course, do all of the easy stuff like checking your electrical connections for corrosion first. Pulling the alt is not hard (should take less than an hour), and then you can take it to AutoZone or Advance Auto Parts to have it tested for free. Their machines cannot pick up every problem... but its a good starting place. Good luck <img src="/forums/images/graemlins/kewl.gif" alt="" />

Thanks Strawmyers! As a followup, have you heard of pulling the main engine relay as a way to check the alternator? My understanding was this would prevent the engine from switching back to alternator power after it initially starts and runs on battery power - thus allowing you to see if the alternator is in fact the problem. I could be way off base here, but that was my impression after doing some research. Thanks again for the info! Anyone else who has experience with this feel free to add your 2 cents <img src="/forums/images/graemlins/cheers.gif" alt="" />

You won't get the engine started if you pull the main relay...

Where ?

Well, the alternator was in fact the problem. Pulled it today and took in to advance and autozone (second opinion), both said it was not putting out current. Troopersphere, I guess I misread/misinterpreted something RE pulling the main relay. I was using the search feature and couldn't find again what I read about that. Anyways, thanks to both you and Strawmyers for the advice. Happy Thanksgiving-

I think I might have found it Cory, but I didn't write down what I used to search for ... can't quite find it again now. But I did see a thread where the guy pulled his main relay and claimed the engine kept running! I can't understand how though... I was a little confused reading that thread, but there was some good info in it... Heck, there's good info in all the posts!

Thanks, and Happy Thanksgiving to you ane yours also!

Well, if there was a short in the wiring or something, it could have been bypassing the relay. <img src="/forums/images/graemlins/confused.gif" alt="" /> Also, (a lil hind sight) if the alt is bad, chances are the bat is almost dead and would have run the truck. I know then when my positive terminal shorted out the truck died.