I own the predecessor to your model!
I own a Hoover PowerMax Supreme S3611. It's essentially the same model as your PowerMax Ultra. Your machine is newer and runs on 9.3 Amps and has the black hose with all controls. My machine is 9.8 Amps and has the same controls.
If I unplug my hose wire from the suction unit, the motor turns off but the red indicator light on the suction unit stays red. What is yours doing when this wire is unplugged and the motor was running? Is your red light still lit on the suction unit?
Did the rheostat thermal shutoff turn your machine off when the issue first occured? The Reostat thermal shutoff control is the round metal piece with clip that rests in a contained space in back of housing behind the motor. Is all wiring to that decent?
Did you pull the motor out of the housing to check all wires including wires coming from hose into the suction unit? On a standard non- variable speed, non system on/off PowerMax it is a 2 prong, t shaped plug to the suction unit. With the variable speed and full machine on/off it is 3 prongs to the suction unit. So you'll have 3 wires coming from the hose lead into the motor compartment in the suction unit.
When you inspected the motor housing, did it look as if the motor has been moving and twisted various wires? I've had issues with a former PowerMax model where the motor wasn't properly installed from service and the rubber gasket wasn't locking into the plastic so as the motor was turned on, the torque turned the motor and eventually twisted and damaged some wires. I've cut the wires below the point of injury and either re-spliced or tied in a new section of comparable gauge wiring.
Many of the wires in my suction unit are snapped into the plastic shroud but some are loose and may rest up against the motor itself. I've owned PowerMax machines since 1997 and never had one where a wire went bad just from resting up against the back of the motor.
I had a Kenmore canister years back that was a standard Progressive with 3 way power switch for the entire machine on the hose handle. It had an issue where when the hose was disconnected the motor would continue to run. I believe Sears worked on the hose when they repaired it but that doesn't make much sense to me.
Do you see any burnt wires anywhere on your machine in the hose handle or main suction unit? The control board in the suction unit is attached to the plastic motor retainer that goes holds the motor into place.
If you have a question regarding wiring I can take photos of my unit and we can compare diagrams!
Possible solutions for you:
-- Fred Stachnich- HooverCelebrity on here used to service Hoovers at an actual Hoover store. Hoover had hose handles of this style starting with the Dimension 1000 so he have some experience with this and may have a solution?
There is a vac shop in upstate New York with tons of vacuums and he may have parts and also be able to help troubleshoot. It would take him some time to find that particular machine in his stock piles but I'm 99% certain he has everything that you would need. Here is his info if you're interested:
C.S. Vacuums
Owner is Chris
315-363-9083
The control panel in the hose handle is part number 47551014 and is listed as available on Sears Parts website for $41.99. I've posted it in the link section below.
The board in the suction unit is attached to the motor retainer. The motor retained for your model is listed as part number 41312048 and is listed on Sears Parts as available also at $71.49. It includes all seals and a new control board.
http://www.searspartsdirect.com/hoover-vacuum-parts/41312048/0020/473/model-S3620/0517/0642000.html
I was surprised by both links having prices and listing them as available so that's awesome! Sears is very good at staying updated with their parts and listed them as unavailable when they get discontinued!!
Let me know if I could help further!! The S3611 that I have is my first PowerMax with the variable speed and full machine on/off. I've only had that one for a little over a year. I've never had an issue with any PowerMax/ Futura/ Windtunnel machine ever having an electrical issue and my family has/ owns SEVERAL since 1997!!
For reference I've attached photos of what this hose looks like. My S3611 machine is the green one on the right in the 3rd photo. The hose on the S3620, BB62's hose will be black in color, just as the hose color on my blue PowerMax S3603-040 the left machine in photo 3.
http://www.searspartsdirect.com/part-number/47551014/0020/473.html?pathTaken=partSearch&q=47551014
