I just swapped my electronics from my RDQ Source One frame to my new OAS 5 v2 frame, and after finishing the swap (Did not do any soldering) the FC is not initializing when a lipo is plugged in (Everything worked fine before the swap) - On USB I can access the FC as normal, but as soon as lipo power is supplied, there's just a dim red light on the FC. I swapped FCs with another working one, and I get the same issue - I have checked the pins on both ends of the wire harness, and there are no damaged pins, and no visible damage on the fets or other components on the ESC. This is definitely an issue with the ESC, as I just tested a fourth FC with this ESC, and still having the same issue. What would be causes of the ESC 'working', but not allowing power to go to the FC? 

All other FCs I tested were Mamba FCs as well, that pair with the ESC ...

Looks like the F55 just passes vcc to the FC.

I know you said you already checked the plugs, but, I suggest checking for continuity between your positive power lead and vcc from the rear of the harness jack, and then checking for continuity between the rear of the vcc pin on the harness jack on the esc to the the rear of the vcc pin on the harness jack on the fc.

It’s just a voltage pass through, so it kinda narrows it down to the harness itself or the jacks it plugs into.

With power disconnected from the ESC and the ESC-to-FC harness plugged in at both ends, use a multimeter to check that you don't have a short (or a partial short) between the VCC and GND connections of the ESC.

If that checks out fine then with a LiPo connected use a multimeter to check that you are getting full LiPo voltage to the FC. Either probe the VCC and GND pins on the back of the ESC-to-FC harness connector on the FC, or probe between a VCC and GND pad on the FC.

Make sure metal rings in the ESC mounting holes aren't grounding themselves to the frame (if the rings on that ESC have an electrical connection with any part of the circuit on the board that is) because that can sometimes cause issues. Make sure you are using insulation gummies to mount it to the metal frame screws.

I think Snow hit it right on the nose, especially since you said you are getting *some* power to the fc (dim led).

I have continuity between VCC on ESC and VCC on FC, and with lipo plugged in I am getting 24.6 volts from the VCC pad (The pins on the harness are too small for my probes), and re-checked every pad and solder point for continuity (No bad spots) - I had already ruled out the wire harness itself, since the same harness has no issues with the other FCs, but I did try the longer harness that came with the stack, and it made no difference - In over a year and a half of building I've never came across this issue before