What is the fuse/relay for the fog lights (Cascadia 2009)

@RocketyMan

 

There isn’t one. It’s powered directly from the SAM Chassis module. If you had access to Detroit Diagnostic Link it may show a code there for open circuit or short to ground. It could also be the switch.

 

Sounds like a bad ground common to all the front lights.
Detroit Diesel Diagnostic Link is the software program used to set parameters and do fault diagnosis for n Detroit engines and transmissions, plus Freightliner and WesternStar trucks.
Cost $500 per year subscription plus under $1,000 for the adapter to hook to a laptop.

 

Just looked at the wiring diagrams. It is way more complicated.
The light switch sends a signal to the Multiplex System Field (MSF) switch. Its the assembly attached to the dash that contains the Four-Way-Flasher switch. That then sends a signal to the SAM cab controller which is located in the passenger firewall. Part of it is behinds the glove box, the other part extends out into the engine compartment. Then the SAM Cab sends the power directly to the fogs lights.
Seeing as both now quit: the most common cause is water intrusion into the SAM Cab controller due to a leaking windshield. This will cause corrosion in the wiring harness connectors that plug into the SAM Cab module.

 

On my western stars, before any truck is put into service, I have a glass company come out remove the windshield then reinstall it with good sealant and a new gasket. Before I did this i would have water pooling on the floorboard and getting the wiring wet behind the dash. They may have fixed this but it gets done no matter what, to depend on the dealer is like waiting for a Martian to come down and fix our cars.

 

I need last 6 of vin.

That's nice the driver's manual was checked, but if more pertinent detail is needed...I need specific information.