OEM Trailer Light Wiring Not Working; Replaced with Hoppy and Still Not Working

[Chaldaean]

Quick explanation:
- Truck came with OEM Lexus trailer wiring
- Recently lost left/right blinkers, but tail lights would still work
- Bought a trailer light tester (like the one pictured below) and got the same result (tail lights okay, but blinkers don't show), so it's not the trailer-side wiring that is bad
- Ordered a "Hopkins Plug-In Simple 43405 T Connector Wiring Kit For Toyota Land Cruiser" from Amazon and just installed it (took less than 5 minutes).
- Same result with the tester (tail lights okay, but blinkers don't work).

What should I look at next?

.

 

[titanpat57]

Grounds...

 

[Mark Harley]

Yep, I would check the grounds on TV and trailer.
new ground loop end clean to bare metal and a new bolt or screw.

 

[Chaldaean]

Great! I'll check that out.

I want to clarify that the blinkers are working fine on the truck; they just don't work through the trailer harness.