Seriously, I was chasing my tail and came to a dead end for the moment. The problem was the overheating relays but I could not find the reason for the overheating except that possibly ALL the relays were defective. (Which I doubt.) If there was some deep-seated problem other than that then I would troubleshoot it another day. Meantime other projects awaited.
From the previous posts on this you will note that I discovered that cooling the plugin board allowed it to operate hours on end without faulting on the display. So, succinctly, I was able to locate a source of 12 VDC (from the other existing fan board) and bolted in a three inch muffin fan I had lying around.
The burn-in testing with all covers and running in a "normal" environment failed to fail, if you will. It ran for eight hours. In fact, I ran BOTH of the frequency counter plugins I had -- the 7D14 and 7D15 -- in the same unit and was counting input signals to beat the band.
Below are pictures for your (ad my) reference.