Rear blower motor

I have a 1991 APV and the rear blower motor will not come on at all. The front blower motor will only come on HI speed. I have already replaced the front resistor. I went through the diagnostic tree and concluded that the controller was bad so I replaced that for $150.00. I know that the rear blower is getting power but not ground. The yellow wire comming out of the auxilary blower motor is hot, but should be ground. All of the grounds for the relays are present. I really don't know what to try next. Please help.

Do you have also a rear control for the rear heater or only a control from the front?
Anyway, boths diagrams here:
www.avigex.ca/xport/hvac_rear_single.jpg
www.avigex.ca/xport/hvac_rear_dual.jpg
ANd the yellow wire IS a HOT when rear relay is energized.

and for front
www.avigex.ca/xport/hvac_diagram_front.jpg
SINce high speed relay needsthe low speed relay to operate also, then th elow speed relay would be OK and I suspect the low speed contact in the high speed relay (unenergized) is shot. BUt both problems would be unrelated then...
Some other common ground could be at fault....