2007 sierra remote start

I have dark blue in brown plug pin 24 at the bcm, neg trip For pos trip, you can pick that up under hood at the fusebox, usually a brown wire but can be light green on some production models. I'll have to double check but doesn't the CM4200 have selectable parking light output?

There is a switch inside the unit you can switch it from parking lights or truck release mode.

Look at a copy of the 4200DX manual that I have, there should be a 7 pin connector with a GREEN / WHITE wire in pin 1. This wire is a neg parking light wire rated at 250 mA. You should be able to use this to flash you parking lights on the dark blue wire. My schematics only show the dark blue wire as a neg signal from the bcm to the parking light relay coil.