No clearance lights on box truck. Computer controls

I have an m2 freight liner box truck, I work heavy duty, and Mitchell doesn’t have a wiring diagram that shows how it’s wired. At least what I get from Mitchell only shows that a bulkhead module tells a chassis module to turn on top clearance/marker lights. Is there any way of starting at one of the lights and working my way back to the module? How would you approach this? All lights work except clearance lights on box truck which should come on with headlights. Thanks

I would say that if none of the clearance lights are working and a module is controlling those, I would be starting at the Chassis module to see if you have power and grounds going to it and if you have anything coming out of it. If not, move back to the bulkhead module. Are the lights one wire or two? You potentially could have a broken power/signal wire or bad ground after the Chassis module as well if your tests of the Chassis Module checks out.

If you can find which light is the first in the series of lights, you could do a bypass test and supply power and ground to the wiring going to this light to see if all of the rest light up. I'm sure they are wired in series to each other. A bypass test may be your best bet at figuring out which color wires are your power and grounds as you make your way back to the Chassis module since you don't have access to a wiring diagram.