relay for rear defrost

This is a simple question.  I want to use a relay to activate the defroster during remote start.  I have searched the relay section and other threads but can't quite find the answer I need. 

I have found the wire going to the rear defrost grid in the drivers kick panel. This wire show 12 volts when the defrost button is activated. When I cut this wire, which side of the cut wire do I connect  to which pins on the relay, and then which pin do I connect the 200ma from the R/S to, and which pin for my 12 volt source during remote start? 

thanks

First of all what is the year,make and model of the vehicle and then what kind of alarm/rs are you using?

87a - factory rear defrost input(from BCM)

87 - 12v+ input

30 - factory rear defrost output(to grid)

85 - 12v+ input

86 - (-200mA trigger from R/S)

putting this in my son's 1998  Chevy Cavalier with a Viper 5301. I have the wire going to the rear defrost grid in the drivers kick panel. This wire has 12 volts when the defrost button is on and goes to 0 volts when off.  And I know i use the blue/white 2nd status/rear defogger output wire on the R/S, most likely in a latched mode.

In looking at the different diagrams and lay outs for relays, it seems to me that 12 volts constant would cross over from pin 86 to 85 and allow 12 volts to go the r/s brain, or two 12 volt sources bucking each other.  Pin 87a and pin 30 as shafferny wrote above I understand, but i guess it's the two 12 volts on 87 and 85 that are confusing me.

Granted I've only used relay before for the dome light supervision, but this application has me confused. I don't want to do something wrong and fry the brain.  I did my taurus with just the 200ma status connected to the input wire of the defrost switch set on pulse.  So i'm looking for experience/expert guidance to steer me through my confusion.  so thats my story and i'm stickin' to it. maybe i' overthinking it.

Thanks All

Ok wire like this

Cut the defrost wire and the side from the defroster (window side) goes to Pin 30

Other side goes to 87a

Pin 86 and 87 is ignition fused at ten amps

Pin 85 to the blue/white defrost wire from remote starter

Also in reference to that guy from greece, What? You put a diode across 85 and 86 band towards 86, Not 87@!

t&t tech wrote:

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Ok wire like this

Cut the defrost wire and the side from the defroster (window side) goes to Pin 30

Other side goes to 87a

Pin 86 and 87 is ignition fused at ten amps

Pin 85 to the blue/white defrost wire from remote starter

Also in reference to that guy from greece, What? You put a diode across 85 and 86 band towards 86, Not 87@!

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Exactly.

When the defrost circuit is active via the R/S, it will isolate the circuit from BCM.

lol i do the same as you t&t.

85 is ALWAYS the ground and 86 is 12v.

Thank you everybody.

After my last post, i went back to read the relay section of this site and it suddenly made sense to me what everybody was telling me. Thanks for your time on this.  I'll tackle this in the morning and wrap it up.

Darn those slow brain cells in my head. gotta quit drinking when i'm doing something important.

Of course,

You guys were right. Connected the relay up as described and all is good with the world.

Thanks once again.  I need to quit over thinking some of this stuff.

Rich