I know I can use an HDMI source like a Raspberry Pi and a small screen for HDMI and could twist copper cable together and measure continuity through them to narrow down which is which but I’m wondering if there is an easier way. Maybe something I connect to either end?
Yes, it’s called a toner. You put one piece on one end of the wire, then go put the other piece on the wires at the other end until you hear an audible tone. That’s how you match them up. Label them after you tone them!
Tone chaser def the best here. Harbor freight (if op is USA) has shitty ones for like $10 that do the job fine.
If you can’t get one a multimeter in continuity mode with some long wire works if you’re tracing in one area. If it’s a huge area or across multiple rooms you can put low voltage on pins and use the meter to check for voltage on the other end. Make sure it’s not plugged in though