Buss bar wire is typically green, and should have a #5 tag on both ends. Understandably you lose you lose it in the wiring harness, but the other end is connected to the HEAT post on the back of the keyswitch. If you have access to a multi-meter, set it to measure DC in the lowest range that will read 12 volts. Put the positive lead on the buss bar, and the negative lead on the negative post of the battery. Have someone turn the keyswitch to HEAT. If you see 12v, your switch and wiring is good. If less than 12v, you need to clean some connections or add a relay and larger gauge wire. If no voltage, either the wiring has been compromised or the switch has gone bad.
//greg//