I'm trying to power my new Raspberry Pi 4 via an external power supply, that only has positive and negative leads coming out of it. So I can set that to 5 volts, but then I need to connect it to the Pi somehow.
The new Raspberry Pi 4 is using USB C. I have a cut USB C 3.1 cable here:
I'm not sure which of the wires is the power in the cable. I thought it would be the red one that doesn't have shielding around it, but when I plugged the other end into my USB C wall wart, I wasn't getting 5 volts on that line when I measured.
So, which wire is power, that I should attach to my variable power supply to get 5 volts to my Pi? And if it is supposed to be the red one, why wasn't I getting power before? Is the USB C standard expecting some sort of handshake to occur before it supplies power? I know the cable was good before I cut it, because I was using it to power the raspberry pi from my USB C wall wart previously.
Or alternatively, is there a better way to accomplish what I'm trying to do? Any help would be appreciated, thank you.
Edit: Ended up just supplying power through the GPIO header. I never got it working with the spliced USB-C cable, and the breakout board I got did not allow enough current for the Pi to run (I should have checked that before ordering it).