Check again for short to ground of the 8v circuit (should show open with C2 disconnected).
I wouldn't expect to see 5v at the signal wire with this circuit shorted, but we've gotta check the basics.
Speaking of which, there are powers and grounds to check. This is the other connector, the C1...
This is where I like to emply the "load device", typically a high-draw bulb such as a headlamp or fog lamp. Either one will suck about 4 amps, more than enough to tell if the power or ground circuit is up to snuff.
Note that Pins 10, 47 and 50 are grounds. Connect your load device to B+ and feed it to those terminals to see if it holds well. The beauty of bulbs are that they display their flow rates in lumens... so if you're blinded by the output... checks OK.
Pin 20 is the ignition switch output, primarily used for a wakeup call to the controller but may also be used for other feeds... not known. See that it holds up as well.
#46 is the B+ feed to the controller... same applies.
While I don't expect the 5v feed to be a problem, you might check Pin 51 just in case. Grounding of this circuit will normally KO the controller, which means you don't get the 5v pullup voltage at the cam or crank sensors. No communication with the controller is possible during those times, either.