Hey all... back again. I've checked every wire in this truck, cleaned nearly every connection and ground in the charge system, scoured schematics for hours, probed voltages at every junction as per the info on this forum and I still can't figure out what is going on with it...

Original issue manifested as a blown 80A fuse after my OEM alternator died under heavy load. I replaced the fuse, then a questionable battery, and it popped again. Replacing the alt with a reman solved that short-circuit issue (B stud was shorted to ground). Success, right?

Nope! The reman alternator died on the third engine start. So did the next four alternators I installed. Every time I saw 13.8-14.3V at idle for the first two starts and they were dead (back to battery voltage) on the third start.. Even the domestically made 160A aftermarket one. At this point I can't blame Chinese quality...

As you may have guessed, I have no f***ing idea what is going on with this truck. I don't understand how my alternators could be dying so consistently when there are no shorts in the wiring and no excessive loads with the engine running or with key on ignition and engine off.

It still will run for hours until the battery drops, but it keeps murdering alternators and I'm out of ideas. Has anyone got any good suggestions here? The last idea I have is that starter may be arcing internally and toasting the diodes... and I'm not sure how I'd test for that.

 

Pictures might be useful to get input at this point.
images around the battery, fuseblock, alternator, etc
What non-Toyota things are installed?

 

Can do... I'll get pics next time I'm working on it. There are no non-toyota bits on the truck at this point. It was DLX cab & chassis dually that was converted to a motorhome. I converted it back to a truck, keeping only the OEM wiring. Had no issues for almost three years. Then I had the wise idea to run a body grounded PWM in the glovebox. It pulled ~25A directly from a fused line off the battery positive. After ~1000 miles with the PWM on, the alternator pooped out while loaded down with lights, radio, and wipers on a rainy day. I removed the PWM and wiring, but my newfound alternator problems still persisted...

After typing that up, I'm thinking I need to recheck all my body grounds for internal breaks in the wire, particularly the one by the battery... a few strands of connection will read good to a continuity meter, and possibly still even read a low resistance, but they may not be as happy when presented with a full charge current...

 

what is a "body grounded PWM"?

 

I was testing claimed MPG improving devices for a mythbusters type video, one of them was an HHO setup that used a pulse width modulator to vaporize water. So it's a device that pulled around 25 amps when in use with the ground wire being to the body via 10ga wire and ring terminal.

 

 

My favorite was putting crystals (yes, quartz crystals) around the fuel line

 

So, it was way stupider and simply than I could have possibly imagined... but someone else already probably guessed it. The charge/sense wire that is switched on with the ignition was tapped to run power to a coil for charging a secondary battery when the engine was running. Leftover add-ons from when it was a motorhome were the gremlin. The extra load on the wire kept the circuit voltage low enough the alternator output was low and the charge light was almost always on.

But hey, it works again! Thanks for bearing with my frustration!