Need help
 

Heater ac rear defogger switch wont work it doesn't light up I replaced the resistor next to blower motor blower motor is good I tested it all fuses are good at its end any help would be greatly appreciated

Check the multi-pin connector that is under the passenger side kick panel. If it's line mine was you may not like what you find (charred plastic and burnt pins). Locate the rear defroster cable in the connector, it will be obvious if charred, Bypass the connector.

Better steps on this thread -> https://montecarloforum.com/forum/fw...-2007-a-41169/

Disconnect wires from the switch to test switch itself ! Set your multimeter to Ohms, ( Horseshoe looking symbol Omega ) Put a meter probe on each tab of switch ( doesn't matter which one on which tab. With switch off you should read 1.0000 or no continuity ! turn switch on you should read continuity 0.0 or maybe 0.3, then switch is good. If it reads 1.0 its bad.
The resistor adjusts the speed of the blower motor and likely has no effect on the rear defrost. usually if this is bad, the blower motor will run full blast or not at all,

If your switch reads good, then you have to check and see if you have 12v coming into the IN wire at the switch ( with switch disconnected ) Switches generally have 3 prongs one marked NO, one NC, and the other PWR. NO Normally open , NC normally closed. are the switch out puts , the other is the power source, sometimes its just two prongs In and out !
If you don't have 12v on the in wire, the problem is between the switch and power source. If you have the 12V and 12Volts comes out of the switch then the problem is likely the device you are attempting to use, or a cut wire in between.