I'm looking for the wire to turn on the park lights at the light switch itself, which in past experience was a brown wire(+). It doesn't respond. There is 12v coming from the alarm brain. Do I have to run a separate wire directly to the drivers park light for this van?

Could you also maybe explain the difference between multiplexing & class 2 Databus systems.
I do realize that the OBDII is a GM standard and is not used in this van and I realize that multiplex system is tapping into the ECM or cars computer to add an external device such as alarm etc

I generally stick to sound and video systems but do the odd alarm or starter

OBDII is not just a GM system. It is separate from Class II Databus. Class II Databus is a system for getting control signals etc around the vehicle. OBD II stands for on board diagnotics and is totally separate, almost all vehicles from 96 on have it. For parklights if you want positive it should be brown at the fuseblock under the seat. You can also get it as a negative, brown/white at the brown plug at the BCM.

Thanks, should make for a happy customer. None of my wiring installation software has any of that info, so I guess this is where experiance pays. Thanks again!

I found a thin gauge white wire coming from the actual relay for the park lights on the fuse box under the drivers seat.

I applied a relay to switch my postive park light wire from the alarm's brain into a negative and tapped into the white wire.

I could not find the positive brown at the fuse box.

I had orginally tried to tap into the back of the light switch but the one wire I found for lights had negative while the lights were off and positive during park lights & head lights. Orginally there was no "at rest" at the parking light wire which made me feel that sending a pulse of positive to this wire might either short out the brain's park light wire or damage the van's electronic switch.