I've got a 3DR Hex equipped with an APM2.6 and a Taranis X8R receiver.
I took it apart a couple of months ago to go over things, check connections, and tidy up the wiring. It stayed apart because the Jan/Feb weather was horrible.. (-15 to -30C with 20-70km winds just about every day).
I just put it back together and there's one connector coming off the power distribution board that I can't recall where it goes.. (It's not mentioned in the assembly instructions.
(As a point of interest, I powered it up my hex with the connector just hanging loose and everything seems to work.. ESC's power up, as well as the APM and the Receiver)..
If you have a 3dr power module, that cable is redundant.
It's 5v when I measured it, so assume it was powering the apm at some point. Perhaps just an evolutionary relic?
Ah.. OK, it all makes sense now. I think I had it connected to the +/- rails on my receiver and I installed it on the receiver rather than on the APM because the APM was connected to the 3DR power module.
But everything seems to work without it, so I guess I'll tuck it away and use it should I ever need a 5V supply for something else.
Thanks for the replies!
Normally when I do a rebuild, I "save" at least 4 bolts, 2 screws, 6 washers, a riser or two, a BEC and at least one "wtf is this doohikey?" component...
Yes, I use that +/- lead to sometimes power the receiver rather than have the receiver draw power off of the APM...just in case. The lead pulls its power from one of the ESC's and should have a steady power supply.