I had an issue with my motordome shop I just finished. No matter what the left gate would not open. Even though it has a test mode. I verified everything was working and wired correctly.
I grounded the transistor tab and the gate operated. This narrowed it down to on the board.
After searching online I found a lot of mention of the issues. Even one person that had three all with he same issue. But no solution offered.
The solution is for you to install a jumper in JW8. I used a 0 ohm resistor. I found the right gate (JW10) had its jumper installed. And the schematic is genric so it shows it open.
So that's it. Verify by grounding the tab on Q9. Then install jumper JW8.
Must have been missed like the factory flasher rewire.