The red wire goes to the + terminal on the coil along with +12V switched from the iginition switch that you pick up off the old switchgear wiring. Use a testlight or meter to find which wire gives you +12V when you turn the ignition on and that's the one you run up to the + terminal on the coil. Make sure you get +12V before the ballast resistor (if you leave it in place) and not the reduced voltage coming out of the other side of the resistor (that goes to the old switchgear IIRC).

__________________
Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz