I have a Honeywell F50E 20 x 25 electrostatic cleaner and Trane XL80 TUD120R960A furnace which are about 15-20 years old. The power light will not light on the F50E power box and the air cleaner does not work. With a test light I found there is no power at the F50E junction box when the furnace/ac is on with a test light in the junction box receptacle. The receptacle checks OK. The junction box is located behind the air cleaner power box which plugs into the junction box receptacle. The door interlock switch does not appear to be in the power box circuit, since the wires come directly from the furnace internal junction box. This appears to switch power to the cells only. I have not check the interlock switch yet. What else should I check?