kicks on the voltage regulator when there's at least 5 volts in the circuit. I'm feeding in 12 volts. I couldn't find out what the max voltage in that circuit should be, but I assume there's a resistor or something that cuts the voltage in half, so they were probably designed for 6 volts.

Feeding 12 volts I potentially could be shortening the life of my alternator, but a voltage regulator is a solid-state component and should be OK with a higher voltage. The other end of the wire feeds back to computer chips that are probably pretty sensitive. They're also not working to begin with, so I figured there's not a huge downside to potentially back-feeding extra voltage into them.