Hi 355cid. Welcome to the forum. Heat in a wire comes from current going through excessive resistance. The resistance will be too small to measure accuratly but you can measure the results of that resistance in the form of a voltage drop.
Use a cheap digital voltmeter to measure the voltage drop between the two wires for that circuit at the switch. Ideally it should be 0.0 volts. The more resistance there is, the more voltage will be dropped. If you find excessive voltage there, look for connector terminals that were overheated previously. It may be necessary to cut them out of the plastic connector body and replace them with individual terminals. I use crimp-type terminals but I also solder them for a better connection. You might have to cut off about 4" of each wire too and splice on new sections if they are hard from being overheated. Hardened wires are very difficult to solder to.
Tuesday, June 1st, 2010 AT 8:23 PM