Relay Activated Pit Stop on 06 Silverado

So I'm outfitting an emergency vehicle, it is a 2006 Silverado extended cab Z71. There is a Federal Signal SS2000SM siren going in, and we'd like to use one of the on-board relays on the siren to activate a pit stop function. So basically push the button, pull the keys and walk away. I have my head wrapped around using the brake power to activate a secondd relay to open up the first for anti-theft, but any suggestions or diagrams would be really helpful. I know lights and sirens inside out, but this alarm / convenience stuff is new to me.

Hmm. Well, to start off with, you'd need three relays just to keep the thing running and the heater on----there are two ignition wires, and one other wire to power up the heater. On top of that, you would need to use another relay to "latch" the first three in the on position. Or, will the on-board relay from the siren make a constant (not momentary) output after you press the button? You'd probably want to have some sort of signal to alert you that the truck is running, especially if your setup isn't configured to shut off after a certain period of time---maybe the parking lights. Personally, I'd say it'll be faster and more relaible just to install a remote starter (almost all of them have a pit-stop mode). You'll have all the relays on board, parking light confirmation, and a timed shut-down.

Thanks for the response. Yes, the on board relay is programmable for constant or momentary. You lost me with the heater part, I assumed the heat / ac would stay on with ignition 1.

no, heater is on a seperate ( orange ) wire, ign 1 ( pink)keeps fuel pump, injectors, and necassary modules on, 2nd ign ( white)turns on the trans pump and he trans module, needed or else you will get trans fault codes as well as damage the trans. as stated better to install remote starter and use their pit stop feature for both ease of install, and security