03 mack granite lighting issues

Check to make sure you don't. Haveca glitch in the ECM. Fromy my understanding thstc is what sends piwer to the light s

 

As unbelievable as it may sound, it could be the turn signal switch. There's an interrupt button on there, and if the connection is bad it could cause the lights to not work.

I had a similar issue where the trailer tail lights weren't getting power. All of the lights worked on the tractor, but not back to the trailer. Mack had the truck for a couple days and couldn't figure it out...but rigged it so I had lights back there. Now, all of my lights come on with the headlight switch as long as the tail light switch is on...and the dash dimmer switch also dims the tail lights. Not sure how they did that, but a new cab wiring harness is more than I care to spend right now and the lights work.

Silly question, but have you checked the other switch that works the center 3 cab marker lights and the trailer marker lights? Not sure how familiar you are with Macks, but if you only turn on the headlight switch, some lights won't be on...but since you say the lights "go out and stay out", I'm going to assume you know about that switch.

 

How did you fix your lighting issue? I have the same issue, same truck and year.