time delay relays

I was hoping you could advise us about 12 volt time-delay relays. All of our vehicles are fitted with two radios and some also have light bars. Unfortunately our officers often leave the radios on when parking the vehicles after events, leading to flat batteries resulting in the vehicles unable to be started: not ideal if we are responding to an emergency. We have previously used a relay connected to the ignition but this is impractical as during events we need the radios to be operational even if the ignition is off. We are looking for a time-delay relay that will enable the radios to operate while the ignition is off and automatically turn off after a pre-defined period, say 12 hours. Does anyone know of a product that we can purchase to enable this? Regards, Warren P HaddockState Communications OfficerFirst Aid ServicesSt John Ambulance Australia (NSW)

I think altronix makes a board that has 2 sets of contacts built into it, you can program it to a set time. The timer is activated by either 12v being switched on or off. Not sure if it will go up to 12 hours though.94 GT Convertable