Imagine if you had some sort of continuity fault in the y harness itself.
- The signal coming out of the receiver enters the single wire OK
- it tries to split and go out the two legs; OK so far
- it goes down the one leg with no continuity fault in that leg; that servo works OK there
- it goes down the other leg, no continuity, no signal/power, nothing happens.
But the wire LOOKS fine on the outside.
I've seen this happen in other wires, not RC aircraft, with corrosion.
Regards