what remote start alarm system are you referring to?
for the viper 550esp and other dei remote start systems, there's a black/white neutral safety wire that needs to see ground before remote start will work. you tap the neutral wire off the ecu. you should put a toggle switch between this wire so that you can disable remote start whenever the vehicle is being serviced or in parked places where you don't want the remote start to be accidentally enabled.
the viper 550esp has a remote start status output that can be used on a relay to 'engage' the clutch to allow the starter to start. this is the blue wire off the remote start harness. this wire can also be used to re-arm a factory alarm, this doesn't apply for this application usage.
when you activate the remote start feature off the remote, there is a 4 second delay after the parking lights flash for acknowledgement. then the system will attempt to start the vehicle.
don't think for a second that you can safely remote start your vehicle by just using the handbrake as the safety mechanism, especially on a manual transmission. b/c the handbrake will show ground even if you didn't fully engage the handbrake. that's just asking for trouble!
i don't have my electrical wiring manual handy with me, so i'll have to get back to you on the defrost option. my guess would to use the Channel 2 output off the alarm. it supplies a ground as long as you are holding the Channel 2 button of the remote. you would attach that wire to Pin 85, Pin 86 is a 12 volt connection or tap to the Ignition wire that's being powered by the remote start Ignition relay, if the defrost button has 2 wires, tap one wire to Pin 87 and tap the other wire to Pin 30. when the vehicle is being remote starter and Channel 2 is pressed, the relay will join the two wires behind the defrost button. this should turn your defrosters on.
Originally posted by quynce
Two questions for anyone that has done this. I am adding a remote start/alarm to my 5mt WRX.
First, I'm trying to figure out the best way to hook up the neutral safety wire. The best I've come up with is with two relays. The first would have have the neutral safety wire on the + side and the status output from the alarm on the - side. Ground to 30 and the alarm's neutral safety wire on 87. Splice 87 on that wire to the - side of the second relay. The + side would be the starter wire. 30 would be one side of the clutch switch and 87 would be the other. There is one potential problem with this setup: I don't know for sure if the status output transmits before or after checking the neutral safety wire. Do any of you know for sure? If it transmits after checking the safety wires, this obviously wouldn't work. The only alternative I see is to ground the alarm's neutral safety wire and just use some relays to bypass the clutch wire during every start, not only during remote starts. The problem with this is that the alarm would try to start even if the car were in gear, even though the clutch wouldn't let it.
Second, has anyone used an output from the alarm to trigger the defrost wire? It seems like it would just require a + or - pulse, but I haven't checked it out yet. Any ideas?
Sorry about the novel, thanks in advance for any help.