redrunner

I have an 89 cherokee and have a small problem. The wires on the back of the heater/AC control unit melted together but did not short out the system. The blower fuse is still good and tested to make sure its not blown. The entire plug is a loss and I don't know which color wire goes where. The colors are blue, green white with a black strip and tan. The pins are in two rows on the back of the switch. Only four wires were connected with the fifth spade blank. I did a quick check to see where power was at and the only wires that tested hot where two wires on another plug. I don't know if power it transferred within the switching system or one of the wires feed the system. I will replace the slip on ends with new ends and make sure every thing is protected. Also do you have any idea which one of these wires caries power in? I never got 12 volts on any of the leads with a test light. I did not take the time to check every thing with a meter but I will get that done before putting it all back together.

redrunner

Fixed the issue...I tore into this last night, by taking apart my kid's jeep just like mine, found the correct location for the wires. Thought it might help someone else if I posted the colors of the wires and the switch location for them if theirs melts like mine did.

Top of switch pins with the control unit installed on a 89 Cherokee
The top
Lt. Blue l upper pin row with three pins
Tan l middle pin row with three pins
BLANK l lower pin row with three pins

l Green upper pin row with two pins
l White with Black tracer lower pin row with two pins
Hope this helps someone else.

Running Free

What made the wires melt? Were you using a higher amperage fuse?

redrunner

no the fan was killing off and drawing more amps than the wires could carry. I cut the plug off or what was left of the plug. It had two holes in it from the heat. I cut all four wire back and spliced on new wire to replace put on new crimp ends and attached them to the new switch.

mcfadyen72

i just had the same problem.
melted wires on the back of your hvac unit is more than likely caused by a blower motor wearing out. the motor wears out and gets harder to turn, therefore drawing too much voltage and cooking your wiring harness. it also causes a lot of guys cd head units to cut out because it overheats.

alpine.adrenaline

Even if you use those crimp-on connectors, that may only be an extemporaneous solution. My old motor was the original from 1987 and it turned my switch housing to goo, so not even the little rocker switch would move. After replacing the motor new and a JY climate control, the switch stays cool and yet it feels like a leafblower's in the dash.

My375hp302

Perhaps you should run a lower amperage fuse to help prevent that from happening again. As wires age they degrade too and the amount of reisstance in the wire goes up which can cause heat build up in the wire itself. Simply replaceing the ends will not solve your problem.

alpine.adrenaline

Anything on one end of the wire or the other drawing more amperage than the stock wiring can tolerate will fry the wire or any lower amperage fuse you put in there. Go ahead, lower the fuse rating- you'll just go through them faster. Furthermore, the reduced conductivity of copper wire as a result of age would not be noticeable unless your switch and motor were several miles apart or it was hundreds of years old. The insulation around the wiring will become brittle and break off before you lose electrical conductivity. The wires would take more damage by trying to conduct more than their gauge is rated for, which is what's happening in this case. The motor is too old for the wiring.
https://www.cherokeeforum.com/f2/hea...melting-36735/