How much time do you have on the tail motor? The BCP repacement tail motors are known for going bad in just a few hours and this can cause other problems, so you might want to try another tail motor on the proper 4 in 1 plug just for kicks. Another thing to check is the TM connector. Unplug the main motor and carefully "wiggle" the TM connector at the 4 in 1 and see if it runs. You can also try turning the gyro gain and proportional mix screws "up and down" a few times and then try the TM again.

Your tail motor may work OK while running off the 4 in 1 main motor plug (due to the higher output current that this plug provides)
and not at all while running off the 4 in 1 TM plug. I went through pretty much the same problems you describe and though that my 4 in 1 was bad (after replacing the main motor). It was, in reality, a bad relacement tail motor that I had installed a few weeks before. I found that the brushes in this TM were completely worn out at less then 3 hours of use. Just my .02 worth.


Good luck and good flying!