car alarm with keyless start

I have a 1995 saturn SL with a Hornet 740T alarm installed.

my alarm has an Aux output that is designed to power relays, etc.

I was thinking of using this to make a keyless (not remote) start.

what i was thinking was to use an SCR to close the three circuits that the key cylinder normally closes when you put it in the "run" position. i would then have a normally-closed pushbutton to open the circuit, thereby turning the car off.

one of the circuits the key closes in the "run" position is the ACC circuit. i was thinking i'd have that of course powered by the same SCR, and that i would also have a switch in parallel so i could run the radio, etc, without the car on.

i need to close three circuits with one SCR, so clearly some relays are needed. i was wondering if it would be best to have the SCR only power these three relays, or if i could have the SCR power one of these circuits, and add two relays in-line.

it feels like i'm missing a detail here, but i can't think of anything. the big question here is does anyone see anything wrong here or any details i've overlooked?

If you really want to do something like this you can use only relays, I don't see a need for any SCRs.

You would need to power the ignition circuit, the accessory circuit, and then apply a pulse to the starter circuit (with a push button presumably). 

You would then need to break the IGN circuit to shut the car off.

-------------
Kevin Pierson

i had the best idea at one point in my life, i found a sent of push buttons from a rollercoaster panel, RED / YELLOW /GREEN, i think those would have been a sweet idea to hook up as a push to start setup in a center console....try maybe looking for something like that...red-shutdown, yellow-ignotion on, green - engine start.