Rookie mechanic: trouble shooting advice requested

Ok...Checking the voltage in brittle old wires isn't something that I am too excited to do but of course, that's what I need to do!! I look at the wires and it just looks like a mess to me.

I don't know what does what...so they should all show ~12v with the ignition switched to the "run" position?

I do have a new ballast resistor sitting on the shelf. It probably wouldn't hurt to just throw that in

Thanks!