When we hook our trailer up and put the truck in reverse we blow the gauge fuse. It only does it when we have the trailer hooked up.
We have a 2004 tundra extended cab 4x4. It only blows the fuse when the trailer is hooked up. It didn't do it to our friends GMC.
Something is wired incorrectly on your trucks trailer plug.
Yep figure out which wire is which on the trailer then the truck and if your going to toggle between trucks pulling the trailer then splice in a connector that is for each wired correctly.
most likely too weak of a fuse for that line OR you have a case of reverse polarization because of the wires being criss cross somewhere as mentioned above Cap Steve. It's not your chassis. When the tongue of trailer connects with receiver it's already in the hitch and that acts as your ground. Definitely a wire issue weak f