94 Pete 379 dash lights not working

Bad ground?

 

Bad potentiometer in the dash. Check it for power in and out. It should have 12v in and the voltage will climb as you turn the potentiometer to brighten the dash lights.

The potentiometer is the knob to make the lights bright and dim, it's a pricey switch but they don't last forever. They work off of a copper to copper contact and over time the connection between the harness and the copper can fry out.

 

379 relay and fuse panel is very prone to corrosion and arcing thatll wreak havoc. Pull the relays and see if the socket is brown and melty. I keep the kick panel off incase i need to get an extinguisher at it.

 

hey having a similar issue with my 379, except my outside running/clearance lights aren't working, but my dash light are.. literally started it yesterday morning and lights all worked, got a cup of coffee and have no lights. my cab clearance lights are on a separate switch and are operating fine, but the switch that power's the dashboard also power's my clearance lights and i can't seem to figure out where or why they're not working.

 

There are two sides to most of those Peterbilt switches. The power will be on the bottom power to load will be on the top. You can have power flowing thru the left side of switch but not the right or vice versa. Or you could have lost power to one leg

 

i figured out that it wasnt in my switch, but had a wire that wore through on one of my bumper lights that was causing it to trip a relay. that power to switch inconsistencies gave me a headache earlier. worst part is i have a master wire diagram, but my uncle repowered the old girl with an e model and most everything he wired up is slightly different than the diagram. anywho thanks for the help.