As far as relays/fuses to check, swap a working relay (like the horn) to the front heater relay and see if that solves it? And for the fuse check the engine control one (30 amp)?

I also have an electrical issue with my headlights being stuck on bright, and my hazards/turn signals blinking rapidly but I think, at least with the rapid blinking, it’s because I have the Laramie SLT which has the quad lights but I installed a set of headlights with only two lamps (I wasn’t aware of the difference when I bought them two years ago). As far as the headlights being stuck on bright I think it might be the actual switch in the dash as I’ve verified the relays work and the fuses aren’t burnt out. Perhaps there’s some other issue with the electrical system causing all of this?

 

Unplug O2 sensor from the connector. IGNORE the oxygen sensor and test at the O2 connector:

Closely inspect the inside of the truck side connector to the O2 sensor. Look for corrosion inside the pin sockets. If you see corrosion, the only real tool to clean is the correct one. A TINY diamond file the width of a needle that can fit in there. ( https://ipatools.com/product/8042-di...o-round-files/ ). You might have some luck with bending the tip of a safety pin so it can scratch and clean the inside of the round pin terminal when inserted

With pin terminal sockets clean:

1) Use a noid light with an incandescent bulb (not LED, they don't have a significant electrical load) and connect the noid light clamp to your +12V battery. Then probe the sensor ground (black/light blue P0132) and the heater ground (P0135 black/white to G105) at the O2 connector while wiggling the harness.
2) P0135 - Connect noid light clamp to battery ground. Switch ignition key On, while at same time probing at the O2 connector the +12V from the ASD relay (dark green/white) you'll get 3 seconds of +12V. Need a second person to switch key On/Off or jumper asd relay terminal 30 and 87 to provide oxygen heater +12V.
3) using Ohm/Resistance of your multimeter, test continuity of socket's sensor output (tan/white - color will vary with each sensor) with the PCM to finish chasing down P0132

If your AC Clutch engages fine, your grounding at G105 is probably OK so don't have to chase down the ground location.

 

I was out of town visiting family for a bit but I'll hopefully get to testing this tomorrow. Drove a couple hundred miles on the truck with no more codes so I'm thinking there's a possibility it is indeed something with the harness/a loose connection. Will report back asap! Thanks!