@alankilian Again, thanks for sticking with me. I've determined that I have a Trex-2 converted to a -3, don't know if + or not.
The black and blue terminals on the interconnect board are for the heater solid state relay, which I don't have, apparently the heater controller has been used alone, not with the software heater control. That make sense? The display is shown in one of the pictures, it is labeled T-REX and has a cheapie red knob. Since the backlight works I assume the cables are connected correctly, there's not much you can do wrong when they are 10 and 12 pin connectors!
So the basic problem now is the lack of characters on the display. Of course it's possible that the unit failed before Phil died but that doesn't seem likely. Or it may be deeper than that, I've tried blindly turning the knob and pushing it, holding down while I turn, etc. Seems like I would stumble into something happening but not so far.
I'd like to go back and try the trex-2 controller but still don't see how/where to connect 24v. After all, I'm in Oklahoma and we'uns aitt tew teknicle.