What is the parameter for throttle pass through?

I’m running AC 3.2.1 on an APM 2.5 in a Trad Heli. I had it working before but after some tinkering and a re-install of firmware I have no throttle. The heli arms and disarms fine but either way I get no throttle response. I’ve been pouring through the parameters but I can’t seem to make find the one that gets the throttle to work.

Let me just add that I have the RSC Mode set to 1 and the Ramp Rate 0, so I should be getting channel 8 to pass through to the servo when armed. but nothing happens, I’m sending input on channel 8 verified by both multimeter and the raw servo data shows the apm is receiving channel 8. but no out put on raw servo data.

Just in case someone has the same problem that I had it came down to:

RC8_FUNCTION

it was set to ‘0’ which is disabled but it needs to be set to ‘31’ for RSC. Oddly enough the version of MP that I’m using only went to ‘30’ in the description which is why I was having such a hard time finding it.