i would have to agree with TennMan, i have seen many electrical nightmares for drivers, when found they are actually contributed to a pinched wire or just a bad ground. It would be best to chase wires starting at the faulty light furthest away from the battery and keep working towards the battery till you find the error(s).
If you need to get assistance with wiring diagrams take the last 6 numbers of your vin to your local Freightliner dealer and ask the parts people for some assistance in getting wiring diagrams.