7 trailer wiring issues

Hello, I have a 2010 tundra and recently my turn and stop have quit working on my trailers (truck is fine) running lights and e breaks work fine. I know turn and stop are powered by the same pins and after lots of troubleshooting this is what I am finding... b4 I start i get the same result if I user the 7pin for the camper or just the 4 pin for the boat trailer. If I shut the truck off turn it on and press the break I get the 12 volts on pins 5 and 6. As soon as I pulg in either trailer the voltage drops to .5 volts. Once that happens I have to release the break shut the truck off and start it again then the 12v comes back. I have spare lights so I clipped on onto 1 and 5 then 1 and 6 withe same result. Again if I shut of the truck voltage will come back. Fuses look fine. Help please

 

If the voltage drop only happens when the trailer is connected you likely have a bad ground.

 

My experience is 90%+ trailer wiring problems are ground. What are you using for ground when testing voltage? Some boat trailers are grounded through the ball but campers are usually grounded to white wire on harness. I like a simple tester light. Start by checking truck connection using the ground on the truck harness. If that tests good you have problems with trailer wiring.

 

You can also take a set of jumper cables and go from the trailer frame to the truck frame. Easy way to test the ground through the trailer wiring.

 

Yep, i will also ground the têster to the trailer

 

Tow/Tail relay was the issue.