No power to HVAC controls and ABS light on - 1998 K2500 454

[Matt_D]

My problems started with a loose battery + connection. The symptoms were the truck was stuck in 2nd gear and no power to tach or speedometer. I quickly went back home and tightened the connection. That fixed those problems. I thought that was the end of it until a couple days later when I drove the truck. Now I have no power to the HVAC controls and the ABS light is on. I have verified all the fuses have continuity, but I don’t have 12 volts to fuse slot 12. It is a 25 amp marked HTR/AC. It is located in the cab on the driver side. Does anyone know if the power to it is controlled through the ECM? Does anyone have any trouble shooting ideas? I am an electrician by trade so I’m more than willing to dig into some wiring but not sure where to start. Any help is greatly appreciated.

 

[Racesmith]

2024 and still no response. I have the issue with no power to the HVAC controls.

 

[AK49BWL]

Fuse 12 is fed power by the ignition switch directly, Hot In Run. It's on a bus bar with Fuse 6 (Cruise), 18 (Brake), and 24 (4WD), all fed by the same source (Ign Hot in Run) -- Fuse 18 feeds the ABS module so that explains the ABS light. The ignition switch is fed by two power sources, both Maxi-Fuses in the underhood fuse block, you're looking for one of the 50A fuses... But, this feeds both the ignition switch Hot In Run and Hot in Accy circuits, so you should also be missing your power windows, wipers, and radio ignition feed if that underhood 50A fuse went out. This leaves either wiring between the ignition switch and the fuse block on the dash, or the ignition switch itself as suspect.