This little light of mine, driver side marker/turn signal illuminated

Weeeeellllllll, more than likely a simple electrical glitch, but what if it's some sort of signal, like flashing clearance lights on a bus? You'd think a 3 year old truck wouldn't have electrical gremlins just yet, so watch out for the black Suburbans. With all the gee-gaws in a truck today, it wouldn't surprise me one bit.

 

When my 17 579 did that, The CCU had corroded. Basically several of the internal switches for lack of a better term started shorting and going weird. Took a full CCU replacment and reprograming to fix the issue. Hopefully thats not YOUR issue. But thats what i got.

 

2021 579, dash lights don’t work sometimes and AC doesn’t work sometimes either. The fix is to shut the truck off, wait 5-20 minutes and start it back up.

 

When’s the last time your cab computer had the software updated?

 

Sometimes that doesn't work either. I've seen brand new electrical parts come straight from the dealer faulty.

I like to use used parts that are already in place and functioning if it's something I can't diagnose or I need confirmation of a diag. Electrical always keeps a man on his toes.

 

Where they bunch the wires together at the bottom of the firewall is another place to start looking. They bundle them tight and tie them to a metal bracket and the wires will rub together inside the plastic loom. Depends on how far you want to dig.

 

If it's just that single light there's a chance it's in the wiring. I've had trailer and pigtail issues do random things like too. One time, it was just a cheap Chinese LED bulb that was screwing everything up.