Where to Wire Defroster on a 02 Astro?

Trying to figure out where to tie in or wire the defrost wire on a Valet 563T for this van.  Can't seem to find any info on the diagrams I have access to.  Thanks for any help.

Anytime I have done this, I use a relay to close the contacts for the factory rear defogger switch. You usually have to open up the heater control panel and solder wire onto the two contacts which the factory switch connects when it is depressed. The advantage is that it only works with the van running and still uses the rest of the factory circuitry and built in timer. It's not too hard in most cases to do this.sparky