04 Burb accessory power on until door open

I would like to replicate the functionality of retaining power until a door is opened for an aftermarket accessory. Does anyone know either:

1. Where a door switch circuit can be found (and is it + or -)
2. Where the power until door opened circuit can be tapped

I am comfortable with building/using relays and just need a switching signal.

by the way - does anyone else have to shut the rear access (lift gate) hard to get it to register closed? Mine does this and I thought there may be an adjustment for the switch somewhere.

Thanks.