how to test negative output on rs?

I want to simulate a button push so I can turn on my rear defogger/defroster. It's a momentary push button switch in the control panel which communicates with the ECU and triggers some relays and stuff. I figured the safest way to not mess with the ECU wiring and everything is to have a relay "push" the switch, as if I manually pushed it. 85: AUX output on RS (-12v @ 250mA) 86: +12v 30: one side of switch 87: other side of switch my logic is if I pulse on AUX output, it will energize the coil and 30/87 will short momentarily, as if I pushed the button. So I wired it up and everything, but doesn't seem to work. I tested my relay by using a different +12v/-12v to energize the coil and it worked, it "pushed" the button. How can I test that my AUX outputs are working? I'm not sure what setting to set on my multimeter and/or where to put the probes. I got the system installed at a shop, just want to hook this AUX up myself. Little bit of learning is good, plus it will allow me to further customize later on (when it's warmer). I have a 2009 Mitsubishi Lancer with CompuStar CM5200 alarm/starter.

red prove to 12v, black to aux wire. When triggered, voltage should drop to 0.

What unit is it...Are you using the correct wire...or on some units you have to press and hold for 3-5 seconds to activate aux... Oh and use the direct current setting...Normally a straight line with 3 dots underneath...The normal switch setting is 20v...M.E.C.P & First-Class

Go slow and drink lots of water...Procrastinators' Unite...Tomorrow!

tedmond wrote: shouldnt voltage be 12v when triggered? red to constant 12v, black to (-) aux output from compustar. when aux is activated, dmm will read 12v.

you're right, i'm not thinking

It's a CompuStar CM5200 alarm and remote starter.  I got it installed at a shop, and I DO NOT have an OP500, but I was playing with the programming menus with 2-way remote.  Do I need OP500 to activate the AUX?

Yes the meter should read 0 volts when the aux is inactive, and twelve volts when the aux is activated! The programming, someone else will assist there!commit your way to jehovah and he will act in your behalf. psalms 37:5