can you externally trigger a car starter?

Hi guys! For a year or so now I've been adding GSM relay devices to vehicles for my friends so that they can start their cars with their cell phones. Normally I just crack open the key fob and wire the relay to the starter button so that when the GSM relay is activated, the starter button is depressed and the vehicle starts. My question however, is whether its possible to directly wire this relay into the car starter? Do car starters have an input wire that allow another device to trigger the car to start? If so what is the wires name? I've been looking at cheap prostarter car starters (the cheaper the better because the key fob remotes are not often used, the vehicle will always be started by cell phone). The have a purple wire called "external trigger input" but they do not explain its purpose very much. Any advice or information will be hugely useful!

I know that DEI starters come with a trigger input, WHITE/ blue I believe. It sounds like that wire on your prostart is the same. The normal use for them is to trigger the remote start from a factory keyless remote, But it sounds like that will work for exactly what you're trying to accomplish.

Excellent! I just got an email back from the ProStart technical support people and they confirmed that when this pin is grounded, the vehicle will be started or stopped based on its current operating state. This makes it wayyyyyyyy easier...trying to solder onto those tiny contacts is murder, and the key fobs are expensive to boot. Has anyone else done GSM related things with their vehicles? i.e. controlling various aspects by cell phone?

I have a 94 lincoln with a command start cs3000remote starter. owner has lost remote. where could i find one. thanks