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Old 08-20-2009
Thread Starter
Join Date: Feb 2009
Location: Olympia, WA
Posts: 8
G&M A/C switch mod question

Hi all,

I was going to do the G&M AC switch mod, but I wanted to use a lighted switch for it. It looks to me like the switch passes 12v to the output- not good when the PCM is on the other end of the wire! The lighted switch has 3 poles: Power, Load and Ground. I'm assuming that if you connected the AC wire between power and load that you would get 12v on it, assuming that there is some path to ground thru the PCM.

Am I correct in thinking this, and that I will blow up my truck's brain if I attempt to use this switch? Any alternative ideas?

Many thanks,
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Old 08-20-2009
WowMike2001's Avatar
Join Date: Oct 2007
Location: Stevenson, WA
Posts: 2,583
Good question actually!

I have some blue LED switches and was going to probe around with a multimeter to find a constant 12v on.. and noticed this does pass a constant current for the most part - Is it safe to just tag into it to light up the switch when its on by chance? Would make the wiring nice and neat for the most part!
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Old 08-20-2009
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Join Date: Feb 2009
Location: Olympia, WA
Posts: 8
12v on the wire

Yeah, so there is 12v on the violet wire whenever the fan switch is sending the demand signal to the PCM. I wouldn't use that for a constant-on 12v. Do you have the power point next to your radio? Power point or cig. lighter are probably your best bet for constant-on 12v.

For my purposes, having 12v on that wire solves all my problems! Of course, I got the LED to light up, but I think I wired the switch wrong- the LED comes on, but not the AC! Moving the output wire from "ground" to "load" terminal, and bringing in an actual ground wire should do the trick. It appears that the ground on the switch is just for the LED, and is isolated from the "signal" portion of the switch.

The LED is so frickin' bright I'm going to have to either color it with a sharpie or put a resistor on the ground wire to dim it down. I wanted an indicator- what I got is a blue map light!
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Old 08-22-2009
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How about using a double pole switch (STDP)... the switch will have two rows of pins on the back controlled by one switch lever.

Us one row to control the compressor and the other to control a a small LED indicator light ?
The power for the light can come from the cig lighter, on a FUSED line and if the LED is too bright add a resistor.

Just thinking out loud, AGAIN !
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