Rear Defogger Trigger

You will pretty much need to go directly to the back of the switch and test the wires to see how they act. That is unless someone has installed this feature on those same cars. Its unlikely though. J Rilla

Owner/Installer

You might get away with finding some kind of negative or positive trigger coming out of the climate control panel on the '99 Silverado. On the Trailblazer, it's pretty unlikely you'll find much of anything there, since much of the car's functions are controlled by the databus, just like the locks. In any event, another good strategy would be to operate the defogger on and off, and try to listen for where the relay is located, and then test the wires there.

In looking for a latching relay to trigger the rear defog circuit using the trunk pop on my starter remote, I came across this product. Fairly small (3x2x1) circuit board, 12v based, accepts + or - trigger, timer from 1 sec to 1 hour, will turn on for time period then off or the opposite, off for time period then on. Many possibilities. Made by Elk Electronics in NC, but you can get them for $28 shipped from www.bass-home.com. I removed the LED, added some long leads, and mounted it below the dash next to the program button for the remote starter so I have an indication that the heater circuit is active. Only downside is that you can't cancel the timer once it starts. I've contacted Elk and asked them to look into this as a future feature.

Ok, this is the second time I have seen a post like this, and it is starting to sound like an advertisement. First your link doesn't work on either post, at least for me. Second, could you not just wire a relay to the power wire for the timed relay and just break power to cancel the timer?Certified Security Specialist

Always check info with a digital multimeter.

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Tell Darwin I sent you.

I've been sick lately, sorry I won't be on much.