Left trailer blinker not working

[Triton owner 123]

The left blinker and break light on my trailer are not working. I know that the yellow wire operates these and it is "hot" coming from the truck and the trailer when I tested them. When I connect the yellow trailer wire to the yellow light wire it goes "cold" and does not work, same with the breaks. I sanded down a small area to ensure the ground is good. I also checked the fuses in my truck for the left blinker and they are good. Any idea why the connection would go bad when connecting the two wires? thanks

[billnorman1]

Poor connection upstream. Could be the flat connector has a dirty socket or a spread socket, could be a bad fuse just barely conducting, could be the yellow wire is just twisted together or has a poor splice. Could be lots of things, what you are describing is known as a "High resistance fault"
Not a ground issue.

[fishnfireman]

You say you have current to the light... My first thought is the turn/brake light is bad.

[Triton owner 123]

I checked it and the light bulb is good. I even hooked up another trailer light but the blinker and brake didn't work there either.

[billnorman1]

You say you have current to the light... My first thought is the turn/brake light is bad.

He does not have current to the light and that's the problem. He has voltage and not enough current.

[fishnfireman]

He does not have current to the light and that's the problem. He has voltage and not enough current.

I know that the yellow wire operates these and it is "hot coming from the truck and the trailer when I tested them.

I miss read this part.. If another light did not work then that rules out my first thought from the way I took it.

[captainrab]

Ok do this. DC is not like ac and sometimes can be tough to shoot. Take a test light. Not a meter and ground at white wire on trailer to yellow on the trailer. If the light fires then you have established that your making a good ground to the trailer and turn signal to the trailer. If not then trace the wires from that point to the truck and correct connection problems. If all is good then begin grounding test light to frame and walk down in 2-3 ‘ increments which will tell you where your loosing the signal or ground. If your light fixture is relying on mounting bolts to proved the ground path, I would look there first. If the ground is wired directly to the white wire that comes from the tongue then the issue could be yellow or white wire but the test light will tell you where the problem is.

The reason I’m telling you to use a test light is that the meter doesn’t actually load the circuit . High resistance connections can cause you to see voltage on the meter but it doesn’t have enough current to actualy drive the load which is why your reading voltage until you apply a load and it miraculously disappears. Hope it helps. Take care

[Triton owner 123]

Update: The initial tester I was using had a small red light, maybe LED and it came on, however the white test light meter did not (thanks captainrab and billnorman1). My next step was to see where the wire in the frame was bad by pulling the yellow ground clearance lights and testing the wire with the white test lamp. It came on all the way back to the rear light.....WTF. Incidentally I was moving the yellow wire quite a bit as i was testing it and the white light came on all the way where it connects to the light. Turns out there is bad connection or something in the last 6-15 inches of the wire in the frame. I temporarily fixed it so the blinker, break and light will work but will replace all lights with LED lights as a winter project. Thanks for all your replies they helped.