Are you sure it's the right footswitch? The LED polarity is different on some of them; only the right one will work - I'm pretty sure it's the one that says Red = Rhythm (although it's a while since I had one). If it is the right footswitch and the LED doesn't light, there must be some kind of problem with the low-voltage supply to the switching network - from memory, there is a large resistor (680 ohms?) that's part of this circuit that can overheat and desolder its connections, or crack and fail - I think it's at the back edge of the circuit board near the power tubes.
