Old furnace- pilot is on but no burner.

:wall: This is a mystery to me. The pilot is lit, the fan works, but no gas gets delivered to the burners, so it fails to heat. I started with the thermostat. I find the fan to work if on. I did the thermostat test, crossing wires W+R, and nothing starts. The thermocouple is keeping the pilot lit. I get low voltage between W and R at the thermostat. And the same on the gas switch before it goes into the metal block. I have even banged on the gas switch to see if I could knock something loose. Nothing seems to work, or even give me a clue as to what is wrong.:mad: I have perused the forum for hours and found more tests to do, but not the solution to the problem. I still do not understand the functional details of the gas switch, and I think I could solve this problem if I could get a description of what each piece does. Or maybe a manual, blowup chart, or any other clue. This monster is so old I could not even tell you what brand it is. But I can desribe it for you. Simple parts. The air flow is horizontal thru the unit, over a plate that is warmed by the burners underneath. The burners have a pilot light, maintained on by a thermocouple. The fan motor is before the hot box, and blows when the hot box reaches the correct temperature. I have replaced the fan motor once. It works much better than the original. The thermocouple is old, but if it keeps the pilot lit, it should not need replacing, right?! And the thermocouple should not prevent the gas from flowing from the main, right?! Please do NOT ask me if the gas line is on. I have half a brain left.