On St. Patty's day, I fired the car up like usual to head home from work and i noticed the voltage gauge jumping all around and it would drop intermittently on the way home causing the lights to dim, loss of engine power, etc. I figured the alternator was on its way out so after doing a ton of research on tech, I ordered a junkyard KG3 2003 truck alternator, with a 1 year warranty. Took an entire week to get here and it came with a bent pulley, YAY! So I swapped that out this past Thursday and I am still having intermittent problems.

I noticed the 24 gauge signal wire was loose and then it fell out of the pigtail. I was thinking that was definitely my problem so I un-pinned the harness and put a new wire in and replaced about 3-4 inches with some 18 gauge power wire. Still, I have problems. I tore apart all (3) battery wires looking for a burnt fusible link, short, damage something and I found nothing. The only fusible links I saw were (3) 16 gauge units on the #2 junction block and they aren't "stretchy" at all, so they should be good. I also traced the signal wire all the way up to cylinder 3 fuel injector and found no fusible link as someone on a past thread swore there was I did, however, notice the wire looked a little stressed and flimsy further up the harness so I replaced my original replacement and added another 6-8 inches of new wire and everything looked good beyond that.

I had some leftover 4 gauge wire from my amp install so I added an additional wire from the alternator to the battery and still no luck. I then unbolted the OE battery wire and utilized only the new 4 gauge wire thinking I may have missed the fusible link or some damage somewhere but still no luck.

I then added a tap to the signal wire and ran an extension up along the inner fender so I could read the voltage of the signal wire to make sure it wasn't above 12 volts. When the engine is running and the voltage is around 14.5, the signal wire voltage is around 11.45. Then, the system voltage will drop for a split second and the signal voltage will drop 1/2 of whatever the system does. So if the system voltage drops down to 12.5, the signal voltage is around 10.45. All of the readings are from my multimeter and the voltmeter on my audio amplifier power fuse (sitting on the battery).

So, I am at a loss as I know the place I ordered this alternator from does a check prior to shipping it out, part of the reason it takes so long to process and ship, so something has got to be intermittently shorting the system out, no? This is driving me nuckin' futz. The battery is about 1.5 years old but usually they will show constant problems, not intermittent gremlins like this, but it wouldn't be the first time a battery has caused some electrical ghosts.

Also, I noticed the alternator I received had (3) wires on the pigtail and I researched that a ton too. All I need for this alternator is the signal wire and it should be OK, right? The alternator doesn't need (2) other wires for reference or anything?

Don't tell me my only option is to trace that 24 gauge red signal wire all the way back to the PCM looking for faults. HELP!

 

Out of curiosity what battery? I am having similar issues currently, and was about to order the truck alternator. My voltage will stick around 14-14.5, then suddenly drop to 12.9. I notice the fans kick on when this happens, but I also can keep it that low if I hit my rear defroster.

About a month ago my battery died, and I swapped to an Optima Red Top. I don't remember these issues prior, but I was hoping the alternator was the cause of my other battery failing.

 

I got my old alternator and "new" alternator checked this weekend. One guy said they were both bad and I took it to another store and they said the "new" one is good. So it looks like I need to go to yet another one to see what they say.

As far as the battery, it's just a regular old Advance Auto battery. Nothing fancy.