Doors Lock/Unlock with Key On/Off

Hello, all. Is there a way, hopefully using relays, to unlock the doors when you put the car in park, and lock them when you take the car out of park? I'm thinking it would need to be a one-shot and might connect to the reverse lights curcuit, as you pass the location when you put the car in gear, and when you put it in park. the output needs to swap polarity, ie: + - to lock, - + to unlock. This will be used on a '99 Tahoe, and an 88 Suburban. Thank you to all in advance. James

I'll try it. Thank you. What about alternating the lock/unlock signal coming from the backup lights positive? James