Today I was looking at some electrical schematics for the Tac circuit. It also shows that the TDC Detector is connected to the Diagnostics plug assembly in the engine compartment, Drivers side. It is a cylinder that screws into a connector, right above the wheel well. I have heard people say that a "plastic peanut" or a cigarette filter stuffed inside will cause the amplifier to make a better connection. This is probably why it went from failing to dead...
Good Luck and let us know how it turns out.