From the ECU, connector 136, pin C18 is the power supply for the heater circuit. Even if my sensors were out of spec, I should see power from that pin. I'll be heading over to a friends house (heated garage) for further investigation, in a little while.
OK, back from several hours of poking around with the wiring and such. When following the diagnostic procedure of the service manual, it indicates a bad ECM/ECU. The results are the same with both of the units I have so I don't think that's it. The pin from the ECM that provides power to the heater circuit is only putting out .3v. Since this power is regulated by the ECM based on coolant temp, I suspect the problem lies between the coolant sensor and the ECM. The coolant sensor has 3 wires, one of which can be traced through the gauge and the data link connector. Another traces straight to the ECM. That one seems to be the likely culprit. Will check that next.