Brake lights

[RWeigant]

I have a Sport Chassis M2 with a Mercedes MBE 900 engine. My problem is that all the tail lights work, but when I hook it up to my 5th wheel, I have no left brake light. Both turn signals work. Here is what I found. At the junction box at the back of my truck, I have correct voltage (13) except for the left stop light that shows 1 volt. The truck left side comes on, but, I think because it LED's low voltage would turn the lights on. I'm sure it's the truck and not the trailer. The voltage has been checked with the trailer unhooked. Any ideas?

[RVhauler]

Has to be on the truck side. I would start tracing wire forward with volt meter

[RWeigant]

I found the problem. Under the truck between the two cab door is a fuse box hidden on the left side. There is four 20 amp fuses there and wouldn't you know the last one I checked was the bad one. It's a bitch to get to, but, it's over. Saved $200.