Odd Signal Electrical Issue (SOLVED)

Thanks for the update!

Glad you found it. Thanks for posting back.

Just want to chime in. Forgot at the time. Problem ended up being the truck side wiring. Right signal wire was cut and corroded to beat hell, along with the trailer charge. It's amazing anything was getting through the wiring at all. Thanks for all the help and ideas though guys.

Well I started from the beginning of the truck. Fuses all good. Relays were doing as they were supposed to chased the wires best I could down the frame and just before the harness that the 7pin connects to. I find a couple of well corroded wires. In a spot that I previously fixed the left turn trailer signals. (Go Figure). Got late but tried with the test light and yup no light blink at the 7pin on the truck but the multimeter pulled the pulse of voltage for the signal. So that'll be tomorrow. I'll let you know.

You might check for the trailer connector fuse. Fords have fuses for each function of the trailer connector.
I know you said you have power at trucks's plug. But you never know whether it is good solid connection.

Thanks for the speedy replies. I'll chime in my findings as I go through all this further.

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.

There should be a junction box at the tongue of the trailer where the umbilical cod connects to the trailer wiring. splice could be bad.
Does the brake light work? Should be same filament if trailer has red turn signals.

Have you check the ground(s)?

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.