Aux channel programming issues with spektrum dx3c
 

Trying to set up shift servo on my twin hammers but not getting very far. Set aux to button e (by the trigger) and selected 2 position switch as I just want to move servo from low to high gear.
Then the problems start. I tried to set end points to minimum in both directions as a starting point and the servo does move as I scroll from max to minimum travel.
When I try the switch however nothing happens, no movement at all. I think it may have moved once whilst trying to work out what I had done wrong but not moved since. Servo is ok as it works perfectly through channel 1 (steering) but haven't tried 2 position switch option on channel 1, perhaps I should try that. I have no reason to think the receiver is faulty but I suppose thats a possinility.
Anyone got any ideas? Much appreciated