Rear Defogger Trigger
Printed From: the12volt.com
Forum Name: Car Security and Convenience
Forum Discription: Car Alarms, Keyless Entries, Remote Starters, Immobilizer Bypasses, Sensors, Door Locks, Window Modules, Heated Mirrors, Heated Seats, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=18098
Printed Date: July 16, 2025 at 6:53 AM
Topic: Rear Defogger Trigger
Posted By: captntech
Subject: Rear Defogger Trigger
Date Posted: August 26, 2003 at 10:21 AM
Getting ready to install two Crimestopper RS900 Remote Starts in an '03 Trailblazer and a '99 Silverado. I'd like to use the trunk pop button on the remote to start the rear window/outside mirror defogger. There is a neg pulse wire coming from the RS900 that will respond to the button on the remote. The switch on both vehicles is a momentary push switch that starts a timer for the defogger. Has anyone done this, and if so, what is the switch looking for? ground pulse or +12v? Also, is there an easy way to tap into the wires to the switch without tearing into the dash and hvac unit where the switch is located? I'm hoping this isn't going to be TOO difficult, especially if someone has already cracked this nut. Thanks!
Replies:
Posted By: jrilla
Date Posted: August 26, 2003 at 7:13 PM
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.
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J Rilla
Owner/Installer
Posted By: Chris Luongo
Date Posted: August 26, 2003 at 8:33 PM
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.
Posted By: captntech
Date Posted: September 05, 2003 at 5:23 AM
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.
Posted By: auex
Date Posted: September 05, 2003 at 8:56 AM
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?
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