Odd Signal Electrical Issue (SOLVED)

jwandvassie wrote:
Based on your tests, you have a very high resistance connection somewhere between the trailer plug and the light. The meter has a very high Resistance so you can read the 12V but when connected to the light, all of the voltage is being dropped across the bad connection.

You should check and/or redo the connection at the plug and at the light. If the bad connection is in between, you may have to run another wire.

Good luck and please report back your findings.

Agree with this. To further narrow it down, check for voltage at the truck, then the trailer plug and further downstream toward the light, all while plugged in or at least with jumper wires between the truck and trailer. Somewhere closer to or at the truck there should still be 12V even with the trailer plugged in. When you find the place it’s not 12V, there’s resistance between that place and the last place you had 12V. If the voltage at truck plug voltage goes to zero, the wiring problem is in the truck.

This all assumes you are using a known good ground (from the truck) for your meter. If you use the trailer ground and its connection is poor, the trailer ground will pull up to 12V and your meter will show 0V.