Rear Review Defroster
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=4684
Printed Date: July 22, 2025 at 9:06 PM
Topic: Rear Review Defroster
Posted By: Vansolo
Subject: Rear Review Defroster
Date Posted: October 21, 2002 at 4:46 AM
How would I install a wire from my remote starter on the alarm of my car to the rear window defroster? Where would I connect the wires, how many wires will I need, and will I need a relay in the process?
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V.Y. LY
Replies:
Posted By: Velocity Motors
Date Posted: October 21, 2002 at 7:56 AM
Most rear defrost circuits draw a LARGE amount of current ( about 30 amps in some vehicles ) so a relay is needed to convert the trigger wire to a larger current power source. You will need to get to the back of the switch where the RD is and probe the wires. When you find the wire that activates 12 volts when the RD is pressed attach the a relay to the RD wire. How did you want to actiavte the RD ? With an AUX channel or with the ACC wire ? ------------- Jeff
Velocity Custom Home Theater
Mobile Audio/Video Specialist
Morden, Manitoba CANADA
Posted By: Vansolo
Date Posted: October 21, 2002 at 11:05 AM
I want to activate the rear defroster when the remote start of the alarm starts the car and deactivate it when I get into my car to step on the gas peddle. So basically I want to connect it to the same wire that starts the parking lights and starter of my car. Would that be the ACC wire then? Hooking it up to an AUX channel would be a alternative choice, but I just want to deactivate it all with one switch. Also I should use a 30 amp fuse on the power lead to the relay, right? How about wire gauges? Would I need to use 12 gauge or 16 gauge is good enough? ------------- V.Y. LY
Posted By: Velocity Motors
Date Posted: October 21, 2002 at 11:33 AM
Use a 5 pin 30/40 amp relay in this configuration: - 86 & 87 : 12 volts constant ( battery connection is recommended )
- 85 : GROUND OUT WHEN RUNNING WIRE on RS unit
- 30 : Goes out to Rear Defrost wire
- 87a : NOT USED
Using at least 12 - 14 guage wire is recommended for this connection for pin 30, 86 & 87. An d use a 20 or 30 amp fuse on the power wire on 86 & 87 as well as a 20 amp on the output pin ( 30 ). ------------- Jeff
Velocity Custom Home Theater
Mobile Audio/Video Specialist
Morden, Manitoba CANADA
Posted By: Vansolo
Date Posted: October 21, 2002 at 11:56 AM
Whao! Thanks a lot Jeff. I've been reading most of the posts here since spring and finally post my first post this morning. This is the best 12 volt info website ever. No wonder it is name the12volt.com.  ------------- V.Y. LY
Posted By: Velocity Motors
Date Posted: October 21, 2002 at 1:23 PM
Thanks for the praise and good luck with the installation ! Post your results when you finish the install... OK.
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Jeff
Velocity Custom Home Theater
Mobile Audio/Video Specialist
Morden, Manitoba CANADA
Posted By: go2pac
Date Posted: October 21, 2002 at 1:37 PM
I also like to add that on most Honda/Acuras, they have a timer circuit with a relay for the defroster and uses a momentary switch to activate it. Other makes of vehicles that have a timer circuit may have the same type of setup. If the remote start unit has a pulsed output when activated, you could use that to turn on the defroster.
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Karl
Pacific Accessory Corporation
Mobile Audio Interfacing Equipment
Connecting You to Your Music Since 1976
Posted By: Chris Luongo
Date Posted: October 22, 2002 at 7:50 PM
I agree with Karl. Test the wires at the defroster switch, and look for one that puts out a negative pulse every time the button is pushed. If your remote starter has a "pulse after starting" output (or something similar), you should be able to attach it directly to the car, and it should activate the defroster.
Posted By: Vansolo
Date Posted: October 22, 2002 at 11:56 PM
Thank you everyone. I probably will be doing this this weekend. I have the relay and wires already. Just gotta pull out my light probe and multi-meter that I haven't used since a long time. Anyway, I will be doing this project on my wife's Toyota Highlander with a Clifford Alarm.
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V.Y. LY
Posted By: Chris Luongo
Date Posted: October 24, 2002 at 4:33 PM
I work on a lot of Toyotas. Next time I do a Highlander, I'll take a quick look at the defroster setup and let you know what I find.
Posted By: Vansolo
Date Posted: October 26, 2002 at 6:07 AM
One more question before I start on my little project. On the same power lead that I will be using to activate the rear window defroster. I was wonder if I can also connect it to the dome light inside the car? You see, when the remote starter is started and when you deactivate the alarm. The dome light will not come as, 'cos of the engine running. So I was just wondering if it's not to much power being drawn form it if I were to wired it up to both the rear window defroster and dome light?
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V.Y. LY
Posted By: Velocity Motors
Date Posted: October 26, 2002 at 8:47 AM
Wire up another realy the same way if you wish the dome light to do the same thing. Make sure you grab the right dome light wire that requires a (+) current.
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Jeff
Velocity Custom Home Theater
Mobile Audio/Video Specialist
Morden, Manitoba CANADA
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