How to reverse polarity in running/ tail lights?

[John in Michigan]

To the OP, CORRECTION from my previous comment: If your LED side marker lights NEVER light up (but the original incandescent side markers worked), suspect polarity is reversed, and you need to swap the wires at each side marker fixture.

[floyd]

Originally Posted by Eggcentric

PS the fact that shore power ground is connected to the frame is of no consequence to the 12V system.

It is in fact consequential since the shore power cord is connected to the converter chassis and the converter chassis is subsequently attached to the frame, a connection which serves no real purpose.

If the Scamp to which I referred earlier had no converter chassis ground attachment to the frame, there would be no 12V reading between the house battery and the frame.
House wiring converters are provided with both fused positive power supplies and negative terminal blocks.
Using them is the best and most reliable approach to house wiring.

House wiring aside...
It is both common and acceptable practice to use the frame for ground for both DOT wiring and brakes. That of course does not necessarily make it the best practice, especially with a fiberglass RV.