A couple days ago on my way to work the voltmeter on my gauges cluster plummeted to 8 (which is as low as it can go) and the check gauges light comes on and chime goes off. The truck continues to drive just fine and the lights don't dim(yet). After work I pick up a Napa alternator and head to my second job. Leaving my second job I needed a jumpstart so i asked security to leave their truck hooked up for another 10 min to let my batteries charge. That lasted about 4 miles with my headlights on. My brother came out with his truck and helped me change the alternator, we finished about 2am. But the truck still wasn't charging. After 4 more leapfrog charges we got my truck home and I spent the next day adding dielectric grease to the alternator cables and plugs, battery cables and still no charge. So having fried my nice voltmeter a couple months ago and the CFO unwilling to let me get another one and just plain tired of not having a working truck I called the dealership and made an appointment. I went outside to hook up the battery charger so the truck could make it across town and when I put the clamps on the posts the alternator wire broke off at the connector! $7 later new cable in place and one more gremlin assassinated.

 

Man, I can almost feel you're pain!! Had EXACT same problem a couple weeks ago but all my wires are intact. Had alternator rebuilt....no fixy!!! Now I'm leaning toward bad (big) cable end or possible ECU problems.


My grid heater cuts on/off like every 2 to 3 sec. and thats not what it use to do. My understanding is that the grid should heat to almost HOT friggin degrees but my grid box is not that hot at all to the touch!!!!

Not trying to hijack your thread but me thinks we might be on to something here!!!

 

Hmm, I have read elsewhere that if you disconnect the positive wire fromm off the heater relay you can disable the heater and see if that changes anything. If that doesn't work (according to various forum posts) it's time to check all your battery(and alternator charge line) cables for resistance issues, more than 0.1 ohm is a problem. One post said to flex all your battery cables and if any are corroded out mid-run, they will flex much easier in that spot. Also checking with your volt meter that there is 13.4 volts at the large terminal on the back of your alternator(but with your newly rebuilt 'nator this shouldn't be an issue). The belt might be slipping was another guess one a forum. Once you've checked all that, my guess now would be the ECM, which isn't pretty because I was afraid that was my problem and when I checked ebay there was a used one for the low low price of $1,299. OUCH! All in all this seems to be a common symptom but the fixes range from replacing the alternator, replacing the serpentine belt, replacing the heater relay or just a simple alternator/battery cable replace. Let us know what you find!

As you can see, without my handy multimeter there were a lot of tests I just couldn't check

 

I had a driver side cable go bad on my 2004. 90 bucks and had to have it shipped to me from 500 miles away. Dealer was on back order, Mfg was on back order as well. Lucky I found one it seems. I also had to replaced the alternator, and batteries.

 

Just want to point out that this test is an important one, and you need to do it with the key off. It verifies that the circuit is intact between the output of the alternator and the batteries. Most importantly, it verifies that the big charge fuse is good. Regardless of whether the alternator is new or old, the test results will be the same.

 

more than possible your grids are stuck on, they draw 90amps each and the alt cannot keep up. disconnect the feed wires to the grids, if they are stuck on, simple check with a test light will show if they are indeed stuck on, also verify main fuze not blown, test alt output at alt and at battery

 

Just an FYI for those that don't know: Alternator reads off the pass side batt, volt meter reads off the drivers side. If you start to have weird charging issues, CHECK the + cable at the drivers side connection. It may be corroded enough to give the alternator a false reading, next thing you know, 18 volts to the pass batt

 

Hmm, I didn't have fuse between my alternator and the (+)pos battery terminal. The previous wire had been customized, should i have a mega fuse in there?

 

Honestly, I don't remember how they did it on the 3rd gens. There is usually either a maxi fuse in the power distribution box, or a fusible link somewhere in line.