So you are using a momentary switch that is tripped at full secondary linkage travel then?
Why not just use the PCM feed from the IMRC harness?
BTW - Anyone with Alex's OBD-II laptop setup can use the signal from the IMRC. IMO that's better since that is what the PCM uses as well. You can also plot it in real time against any of the other PCM data too (TPS, LOAD, RPM, etc)