Originally Posted by dgmelp
...I noticed my speedometer and odometer were dead and then I noticed my outside marker lights were off. After stopping and checking, I found my taillights were off, all outside marker lights were off. The only working things were my headlights and my brake lights.
I found a blown fuse in the under dash fuse box ( number 5 -20amp) and replaced it. As soon as I pulled on the headlight switch, the fuse blew again. I did this again and the fuse blew a third time. ...
From what you tell us, fuse #5 protects the circuit for the tail/dash/marker lights and maybe something else. The key point I'm seeing is that the fuse doesn't blow until you turn on the switch for the lights.
Do you have a toad connected? If so, disconnect the cable and try another fuse to see if the short is in the coach or the car. If not, inspect the 7-way socket for physical damage. See if the cable going to the connector is exposed under the coach and may have been damaged by some road debris.
Do you recall working on anything after the last time you know the lights worked? My thought here is something was opened/closed or moved where a wire for these lights got pinched.
From here on it gets harder. It could be any lamp socket or the light switch itself, or anything connected to that circuit that is energized when the tail lights are on.