servo problems!!

[Brian in PA]

So, I need to put a stronger servo in my triaxle for the steering. I have the stock airtrionics servo in there. Now I have some traxxas 2075 digital servos in another truck. These servos work perfect in it, with a spectrum radio. So, I put a 2075 in the triaxle (after spending 1 hour to tear it a part and replace it) I try it out and nothing happens! I try another servo in my MFU and it works good. I try a different 2075 and it doesn't work either? I try in with the old truck and it works fine. Back to my tri axle and nothing! I am running a RDS 8000 and MFU in my tri axle. WTF am I doing wrong?

thanks!

Brian