Had a brain wave last night with the chiller I just built. I had a power strip laying around that has a motion sensor attachment with an override switch. I wired the thermostat across the override switch and now I have some Christmas lights in the bottom chamber that come on when the fan is on.
I wired across the "B" and "W" terminals of the thermostat, whatever they are. I just found two points that shorted together when Heat was on but not Cold. If I can find something a little more robust than the tree lights I'll be a happy bunny.
I had been leaving the lights on and letting the fan switch only but the chamber would creep up with the fan off and I had to manually unplug the lights. At least now I can walk away from it.