First the throttle linkage and cable has nothing to do with the shift interrupter.This is operated by the shift cable/linkage. Take a meter and disconnect the connector and check switch to see if its open, then depress plunger and it should be closed. If it passes then reinstall into bracket. It only works when you shift out of gear, the clutch dog is held in the gear due to load and 5 degree cut. When you shift the cable actually binds and causing switch to pivot in bracket and trips the plunger, this kills one bank of cylinders,which reduces load and cable pops it out of gear. If plunger is depressed when in neutral the shift rod or cable is out of adjustment..