Alright, I have just put in a new (reman) alternator in the truck thinking it would solve my problems. It didn't...

The problem I'm having is the voltage gauge reads ~13 to 13.5 volts at startup. Once running for a few seconds, it drops down to 12v. Voltage at the battery posts, and alternator post are both a healthy 14.3V, so the alternator is good. Truck off, battery reads 12.2V after sitting for a few hours. So one would figure it's just the gauge, right? Nope... Something bigger...

When I push the brake pedal dash lights dim drastically for a split second, as do the headlights. When I put the truck in reverse (not when the trans engages, but when the lights go on) lights dim. When I use the turn signals or hazard lights, dash lights dim, headlights do not (or not noticeable enough).

From what I see on the alt, there is a wire going to the battery, my upgraded 4 gauge wire going to battery, and another ring terminal attached to a black wire. I'm not sure where this goes, I lose it's path when it goes under a bunch-o-crap... lol

Grounds all look to be fine, and resistance on any I have found measure less than 1 ohm, which is good from my knowledge. What I am thinking is that the main power wire going into the fuse block is the culprit. Things dim, but the battery and alternator are happily humming away at 14.3V dipping only .1V when things are turned on, but rebounding VERY quickly. My question/problem is which wire under the hood is the main power supply wire for the distro block? I haven't found any distro blocks under the hood... Maybe I'm blind?

Anyways, it's a 97 jimmy 4x4 4 door.

Thanks for any help!

 

Try a load test on your battery at your local auto parts store, they will do it for free.

 

Load test has been done on alt and battery. That's why I went and bought another alt. The old one wasn't failing, but it was borderline. Battery passed with flying colours... It's only 2 months old.

Question... Most cars have a single power cable that runs from battery to starter to fuse block. I may be getting confused by extra wires I see, but is it the same with these trucks?

I have yet to get at the fuse block to test voltage at main post there... Too busy at work, and just too damn hot to stay out in the sun...

 

Ok, so I finally had time to dive into it and diagnose the problems...

First I checked voltage at the fuse block while truck was running. It measured 12.7V, not acceptable...

So after looking and cursing for this "hidden" junction box, I found it. Yeah, I must be blind lol. I took off the cover and measured each post. All posts showing 13V +/- .2V, Alt and batt still showing 14.3V.

I thought maybe it's the wire feeding the block? Disconnected everything, and testing resistance on the wire. The alt to junction wire tested 0.4 ohms, so that wasn't the problem. I then tested the box itself... After cleaning each post off, it was measuring anywhere from 20-45 ohms resistance!!! Upon further inspection, it looked as if the main power wire had overheated, the plastic backing was slightly melted where the wire sat.

Hoping for the best I thought of ways to fix it up. I came up with this solution...

I used a junction block that I had sitting around in the garage. It was a tsunami block (for car stereos) that had a 4 gauge input and 4 8 gauge outputs. I ran a separate 8 gauge wire on top of the existing one from the alt to the junction block. I cut all ring terminals off, exposed fresh bare copper in the wires, and put them in the block (block has set screw terminals).

I am happy to report that for the first time since I've had this truck, the voltage gauge read over 14V!! Yay!! Tested out headlights on, fan full blast, hazards going, wipers going, and repeastedly pressing the brakes. Slight dips in the gauge, but bounces back up over 14V. No more dimming of lights either!!

Hopefully anyone with similar problems will find this helpful... Now, on to installing the boom boom I have missed soooo dearly! lol