I pulled the controller out and opened it up. All the fuses were good, all the relay's coils measured good, and all but one of the 20 or so diodes measured good.
The one diode that didn't is a Schottky Barrier diode, 1N5821 rated 30 volt @ 3 amp. I have electronic parts stock and happen to have several 1N5822 diodes which are 40 volt @ 3 amp, same family so same functionality but with higher voltage rating. Replaced that and also the LM555 timer device on that board because it didn’t measure to my liking.
The diode was open circuit so that definitely needed replacing. I didn't find that HWH AP17403 controller listed anywhere so it would have needed to go to HWH's rebuild guy I suppose. It's that black device in the lower right with the 1N imprint.
Anyway, replaced that diode and all is well. The most difficult part was crawling under the dash.