I just got back from a trip, I let a "buddy" of mine drive my 1999 Explorer while I was away. Old battery went kaput while I was gone, and he decided to throw another one in, at night, and in a hurry.

Long story short, alternator gone, radio fuse gone.

Luckily, the alternator was under warranty, so I replaced it, car ran fine for a day or so. Car wouldn't start after I last parked it, so I had it jumped, it died almost immediately after I disconnected cables. Had the alternator tested, it failled. Oreilly's was generous enough to honor their warranty, and gave me a new one.

Now, maybe the alternator they sold me was bad from the get-go and I was starting from the new battery, but more likely is the fact that something is fried somewhere, and I'm not quite sure where to start.

Before I even think of installing this new alternator, I'd like to determine what destroyed the last one. In case it is helpful, the check engine light is not on, and all of the truck's superficial systems are working just fine, lights, horn, wipers, radio, heat and a/c. I've looked over and over at the fuses in the distribution box and on the driver's side, but they are all good (visually, at least, I'll buy a meter tomorrow morning.)

Any ideas? I don't think Oreilly's is going to throw me a new alternator every two days for very long.


Edit: Alternator tested at 28v. If that's helpful. and battery light was illuminated.

 

connecting backward would effect the alternator and possibly computor / processors type equipment. Everything that controls the charging is inside the alternator. I dont see how anything elsw would be effected. If you lost a ground or hot wire, etc, it would not charge at all. NO reason connecting backward would damage wiring

 

Load test the battery for a shorted cell...

If the alternator is pushing 28vdc, it is running with no load....Philip

 

I plan on testing the battery before I do anything else, but there are a few things that strike me as odd...

When the alternator was hooked up, after the last jump, the battery was stone dead, not only not enough juice to turn over, but not even enough to give me the seatbelt beep. I just went outside to roll up the window, and I hooked the battery back up, hoping there was enough juice to roll up the window, and to my surprise, it had enough power to run a/c, windows, lights, radio, everything...


And I also noticed that the battery light, which had been on since the new alternator was put in, was no longer lit....

I don't know if any of that is significant, because my experience with cars is limited mainly to turning wrenches, not troubleshooting electrical issues...

Could it just be that they gave me a rebuilt alt. with a faulty regulator? I'd hope to hear that that's the only reasonable conclusion, but I fear the electrician will pop his head in soon and put my hopes to rest.

If this is all irrelevant, then disregard this, lol. I'll check the battery tomorrow afternoon.


And, to clear up confusion, the alternator was removed from the car and tested on Oreilly's tester.

 

If you have a decent battery charger, you could connect the charger to the battery with the alternator removed/disconnected, then monitor how much current the system draws from the charger. You might want to remove the battery and charge it first. Assuming it charges fine, install it back in the truck and connect the charger. If after a few minutes it's still drawing a large amount of current, there is an issue somewhere downstream. Start pulling fuses to isolate the circuit that is providing the draw and being to zero in on the issue from there.

-Rod

 

Check for continuity on from the alternators charging post on the back to the battery positive terminal. If there is no continuity, it means the fusible link has blown.

 

Ok, I haven't put the alternator in yet, but have some things to add/ask...


Firstly, I got another rebuilt alt, had them test, had my battery charged/tested..

Let the battery sit out of the truck overnight, got 12.6v when I checked in the morning. I hooked the battery up to check for power drains, and was happy to find that there weren't..

I checked for alt. charging plug for continuity, and got it...I didn't check ohms, my meter has a continuity setting.

So, do you think I'm good to try this alternator now? Could the megafuse still be an issue? I'm not quite sure how to check it....Does continuity to the charging plug verify that it is good? Something that concerns me, an electrical noobie, is that when I check the two posts near the megafuse, I only get continuity from one side....The terminal closer to the front of the truck has continuity, but the further one doesn't...Is it just a ground?

 

So the continuity test you performed on the alternator connector, was that to the battery terminal or between terminals on the plug? If to the battery, that would suggest the fusible link is good.

When you tested continuity of the megafuse, are you testing at posts that are part of the mega fuse, or can you tell if they are connected electrically to the megafuse? If they are connected electrical, you'll want to be certain that when testing continuity you are doing so with the battery disconnected. If testing continuity with the car battery connected, you could damage your meter.

A fuse that's good will have continuity through it, so with the battery disconnected, and assuming those posts you mention are connected to the megafuse, one to each side, if you only have continuity to one side, that fuse is open (ie: bad). If you're lucky that fuse blew because some high current reverse polarity feature did it's job. If you're less lucky, a lower current reverse polarity diode did it's job, but now is shorted itself and will continue to blow fuses until you find that shorted diode and replace it or the module it is installed within.

-Rod

 

Just wanted to stop in and say thanks to Rod and everyone for their good ideas and explanations.

Megafuse was the last thing I had to replace, it was in fact bad, now everything reads the way it should. 12 or so volts from bat. with car off, 14.5 or so with car running.

All in all, this goof cost me two alternators, a few cheap fuses, and a giant pain in my *** for 2 weeks.

 

I'm glad to hear it all seems sorted out now. Good luck, and thank you for keeping the forum updated with what you've found.

-Rod