Have you used your tester to compare your wiring on the plug you installed on the motorhome to the one on your pickup? I see a lot of people wire them in reverse since they are looking at in reverse when wiring it up. Start with only park lights on and ground to the ground location on your trucks plug then test the same on the motorhome and compare. Ground to the plug not the chassis to make sure the plugs ground is good. Are the locations the same.
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