99 to 02 Silverado Rear Defrost w/Remote Start

I have had a remote start on my 2000 Silverado for some time now and everything works great. I just have not hooked up the rear defrost yet. I have the factory manual and wiring diagram from GM. The diagram does not get specific enough on the internals of the rear defrost timer/latch. Diagram shows three wires on the timer/latch 1. 12v + in run 2. 12v - ground 3. 12v - output to rear defrost relay there is also a circuit outside the timer/latch going between the 12v + to the 12v - (output to trigger relay) with a resistor and a led on it. This circuit illuminates the LED defroster status light. The defroster activation switch shows to be a momentary switch with 2 terminals that are on the timer/latch but that is all the diagram shows. I would like to have the defroster activate with the remote start, but have it activate through the timer/latch so it is only activated for the pre-set factory amount of time. I have not taken apart the HVAC controls yet (this is where the rear defrost switch and timer/latch are contained) I do not believe the defrost activation switch has any "wires" going to the timer/latch rather it is part of the timer/latch itself via a circuit board. Any ideas on where to connect for remote start rear defrost activation via the factory timer/latch? I have identified the 12v- signal wire going from the HVAC controls to the rear defrost relay. It is a white wire found in the HVAC controls wiring plug. I know I could wire to that 12v- trigger wire but I loose the factory timer function. I have not tried yet, but I believe if I connect to the 12v- trigger output with a pulse from the remote starter it would not activate the factory timer/latch. Is it correct to say if I connect to the white 12v- trigger output I will have to set the remote start to supply a constant 12v- signal to keep the defroster on? Or will it cause the timer to activate receiving a ground pulse on the output side? Any help is greatly appreciated.

On the earlier GM defrost switches you could pulse a relay connected to the input and output of the switch to activate the switch. To test this use a jumper to connect the 12v(-)output to the ground of the switch for a split second to see if the switch activates. If it turns on then wire the relay as follows at the switch 85 to 12v(+), 86 to negative pulsed output from R/S, 30 to ground, and 87 to 12v(-)output. If you are adventurous and want to take the switch apart to solder the one needed wire to the switch internally would be the only engage switch timer option but its not with out risk of damaging the switch to get it open and being able to get the wire out with out getting in the way of the function of the switch and getting it back together. Otherwise you will need to use the (-) latched install bypassing the timer in the switch. Let us know how it works out.

lurch228 wrote: If you are adventurous and want to take the switch apart to solder the one needed wire to the switch internally would be the only engage switch timer option but its not with out risk of damaging the switch to get it open and being able to get the wire out with out getting in the way of the function of the switch and getting it back together.

I saw this post and wondered what the original poster ended up doing. I ended up deciding to open up my switch and found it pretty straight forward. I removed the 3 front knobs and the 4 corner screws on the back of the housing. The momentary switch has 4 solder connections that are in a box formation. The 2 outer connections are common to ground. The 2 inner ones are also connected. I took a small wire, twisted the braids and formed a hook on the end. Then soldered the wire to one of the inner solder joints. This wire was able to be triggered by my unused 250ma (-) trigger trunk output from my Compustar DC3 module. No relay was needed doing it this way. After remote start if I want the defroster on I can just press the trunk button and it comes on and runs for the timed amount of the factory circuit. It can be toggled back on or off via the regular button as well without issue. Just thought others may be able to benefit from this info.Steve G