John I'm not quite sure I follow your knock sensor code theory but will relate my experience for what it is worth. My 93 has about the same miles on it as yours and was turning on the SES light fairly often, the code set was for the knock sensor.
On mine it seemed to happen shortly after start up and I never intentionally drive the car when it is raining so know that was not a factor. The light would then go back out and remain that way until after another cold start.
I should also mention the light always came when driving normally, not pushing it and certainly not at high piston speed.
I checked the sensor circuit and the supply voltage was correct (seem to recall 5 volts?) The resistance of both sensors was within specs but they did have different values, don't recall the readings.
My first thought was a bad connection at one of the sensors but I couldn't get it to set a code by wiggling the wires. I replaced both connectors on the theory that new connectors were a cheaper guess than the sensors, that guess was wrong, still did the same thing. Such things annoy me so I eventually ordered two sensors and used the replacement as an excuse to change the antifreeze. Replacing them cured my problem, I have no idea which one was the culprit but at least it is fixed.
