Ok. Three alternators. Voltage Gauge drops to zero when heavy draw. Any ideas? Just starting a major road trip. Thought replacing alternators would fix it. Truck is an 04.5, electric fans, 5% injectors, stage 2 cam.

 

Check your battery connections very carefully, take them off and clean them even if they look fine. Have you load tested the batteries? I think the ECM reads voltage off the left side battery, your alternator is ECM controlled. Wouldn't hurt to swap batteries from left to right and see what happens.

 

I'll try the battery swap.

New positive cables. New ends on the negative cables. Soldered ends. New alternator to battery cable. New batteries.

I can watch the voltage through the OBDII as I drive (edge insight), and it never goes above 13.5 however when there is a load it starts to drop, and when it gets to the low 12's, the alternator turns off.

 

Ok. Solved, I think.

Changed the wire from alternator to battery to a 1/0 cable. Voltage up, truck running awesome. Thanks.