rear defogger

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vietxtlife

Member - Posts: 10

Joined: November 27, 2011

Location: North Carolina, United States

Posted: September 02, 2014 at 10:04 PM / IP Logged

I want to use relay to turn on my rear defog with my alarm, i tested the wire for the rear defog when defogger off its show +12v and when it on then its show - ( nag). Is there a way to wire the relay to normally output + (pos) and when the alarm pulse -(nag) signal then relay switch the output to -(nag)

howie ll

Pot Metal - Posts: 16,466

Joined: January 09, 2007

Location: United Kingdom

Posted: September 03, 2014 at 12:13 AM / IP Logged

It appears you have a NEG (-) switching line there. Try pulsing that wire to ground with the engine running, it will either be a momentary (pulse) or a constant. If so you won't need a relay.

It might help if you posted vehicle make, model and year.

vietxtlife

Member - Posts: 10

Joined: November 27, 2011

Location: North Carolina, United States

Posted: September 03, 2014 at 1:31 AM / IP Logged

Its 2009 toyota camry, i have thought about that but the alarm only supply -200mv to the wire. I dont think it will be enough to turn on the rear defog, i have thought about using relay to turn weak - ( nag) to stronger -(nag). Question is when the coin not energize what does the out from the relay supply?

vietxtlife

Member - Posts: 10

Joined: November 27, 2011

Location: North Carolina, United States

Posted: September 03, 2014 at 1:34 AM / IP Logged

vietxtlife wrote:

i meant -200mA

howie ll

Pot Metal - Posts: 16,466

Joined: January 09, 2007

Location: United Kingdom

Posted: September 03, 2014 at 1:43 AM / IP Logged

Cut the wire and meter it.

You should be OK if it's a thin wire, it's already triggering a relay.

Simple test, do you have a test light, NOT LED. Then run engine, one end of test light to ground, probe end to wire. If that triggers the defrost, then so will the alarm's output.

vietxtlife

Member - Posts: 10

Joined: November 27, 2011

Location: North Carolina, United States

Posted: September 03, 2014 at 4:08 PM / IP Logged

I have the powerprobe and its can supply + or -, so i try to supply the suspected wire with - and i can hear the defogger relay click. So now do i need to cut the rear defog wire and tide it to my alarm output, or just connect to it without cutting. Still the alarm output a weak - dont know if that affect anything?

sparkie

Platinum - Posts: 2,061

Joined: November 06, 2003

Location: Canada

Posted: September 03, 2014 at 6:55 PM / IP Logged

What output are you using from an alarm? The rear defogger can only be used with the vehicle running as it draws a lot of current. Is the system designed to give a latched or timed negative output? Some remote starters are designed for this function, but alarms are not. That vehicle needs a latched ground on the Green trigger wire.

sparky

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rear defogger

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