I just got a modded Cougar and the RNG rotary is spiking. Opened the throttle, no cripmed/cut/tangled wires that I can see, and the connector is on properly. Any suggestions on fixing this?

The Cougar is NXT2 and HALL modded for both throttle and stick, and when the RNG rotary is rotated full left/right, it interferes with the stick and the analyzer shows input to the left, then up and to the right, then down and to the left, sort of oval pattern with the lower tip on the left X axis and the upper tip on the upper Y axis. I've seen this before with my old Cougar but that was because the rotary was hitting the dogfight switch when closed. This one, even with the throttle handle open, it keeps on spiking.

Disregard, mis-read your post

Had the same problem with ANT pot i had to shut down the involved axis fro control center until solved, you can try to clean it wit contact cleaner but i suggest you to buy a replacement form TM.

Yeah, I thought so. But I am curious why a bad rotary will affect the joystick? Note that these aren't the default joystick pots anymore as it's been modded to HALL sensors, but still affects it like the normal pots.

I don't know how to explain it technically but i think that faulty pots tend to leak or cause voltage spikes that are picked up by the PCB. One thing i noticed is that hall sensors seems to have a "faster feel" when connected to the BU0836, maybe due to less filtering needed, is possible that cougar PCB filtering capabilities are overloaded when a faulty pot is connected and they give false spiking on unaffected axes. When my ANT pot was busted there was no way to use the other axes until turned it off.

I'm sorry, I didn't read your post correctly. I over looked the part where you said the rotary is causing the stick to spike.

Check that the ground wire is attached.

Ground wire -- is that the small yellow wire with round metal parts at both ends? I was always confused where to put these... one goes anywhere on the throttle metal, the other goes to the PCB? Or to the base metal?

Yes to all, bare metal it can't be painted.