Truck-Trailer Wiring Problem -- Suggestions

[jpothof]

Group-

I read a lot more than I post here, but have a wiring dillema that I can't get my head around. When using our normal tow vehicle a 2006 5.3L V8 Envoy Denali the 7 to 5 connector hooked up to my 2010 Ranger 621 works just fine. All lights work as they are suppose to.

I wanted the option of using our 2002 Blazer in a pinch so I put on a 4-5 flat connector and hooked up the trailer. The right stop and turn light will not come on.

I left out the 5-wire adapter and the problem persists

I tested the current from the green wire (R stop and turn on the Blazer), and the tester will blink on the vehicle harness and on the trailer harness as far back as I can follow it to the light. I replaced the truck end plug as it seemed corroded a bit, but problem persists

I thought for sure the ground was bad so I replaced the ground completely on the truck right next to the old ground by filing off the undercoat and drilling a new hole and attaching the ground wire with a screw. This didn't help.

Grounds at the trailer tongue and that right light look great with no loose bolts or corrosion.

I'm not sure if its an amperage issue from the Blazer that the Envoy doesn't have or if I'm missing something. Any thoughts from the group?

Thx

Jeff