PS,I see two pipes. The one furthest from the pool wall has suction, nothing from the other.
This most likely means that your main drain is connected into the bottom of your skimmer... For all practical purposes, this means that you have no operating main drain.. Not a big deal, as you don't really need it..
Assuming the above is true, then most likely your 'bad' pump gets its water from the covers that are in the side wall of your pool..
I don't know much about your bad pump, but would assume that the shaft seal is bad... along with it not running.. If it 'hums' there is a possibility that the start cap is bad.. Normally found under the hump... That said, at this point, I would not spend a lot of time working on it.. Up to you of course...
I think @JamesW has a pretty good handle of your style of pump...
I took a quick look at your "SunTouch".. automation.. Tell me how it is set-up to run now???
Does it now turn the pump on and off via a schedule? Does it change the pump speeds?? Are you using it for anything?
How many hours a day does your pump run? What is the output of your SWCG set to produce??
Thanks,
Jim R.