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I lost my brake and truck running lights while plugging in a trailer that was not wired the same as the truck. Any ideas? All the fuses seem OK. It's a 1994 CC Dually diesel.
Have you checked the fusible links? They're near the battery.
If all else fails, get a Haynes manual and start tracing the wiring diagrams.
I did the exact same thing a while ago, and it took out my fuel pumps (I'd taken the electric brake power off the fuel pump relay - that's a no-no!). I pulled the book out and started tracing wires until I found it.