Flashing D4 light fix?

Hi:
A couple of months ago, I asked for help regarding a problem with our 92
accord 4-cyl automatic (120,000miles).
The D4 light kept flashing, and the transmission shifted erratically.
There were no error codes.
From the research I had done, apparently it was a common problem with
the 92s. The consensus was that the Transmission Control Unit needed
replacing. I bought a (used) one, and it was no better.
I disconnected the Throttle Angle Sensor, the Lockup Control Solenoid
Valves, and the Shift Control Solenoid Valves, and checked the voltage and
resistance. Everything read within limits. Sprayed the connections with
contact cleaner and re-assembled. Pulled the backup fuse for 30 seconds and
tried it, and it was no better. For the heck of it, I stuck the original TCU
back in, and the transmission shifted perfectly! No D4 light, either.
There must have been a bad connection in one of the plugs I
disconnected, and the TCU I bought was apparently no good. The fix didn't
show up until I re-installed the original (good) TCU.
It was a very frustrating exercise, but also very rewarding. I hope my
experience helps someone else with this problem.
Tom