Code 452, no VSS input

My van has a Quigley 4wd conversion. My manuals for the unconverted van show no second VSS (only the one on the rear diff). The manual schematics show the rear diff VSS signal passed to the PCM through the PSOM modual. As I mentioned before, the hole for one near the ouput shaft is plugged; no sensor. There is a sensor on the transfer case (it's a Borg-Warner 1356 I believe) that was installed by Quigley but the Borg-Warner documentaion shows this sensor to be a 4wd indicator light. Is it possible that the indicator light sensor was replaced with a VSS? The speedometer stops working if I disconnect the VSS on the rear diff so there must be a second one somewhere but the only thing I can find is the sensor on the transfer case. Is there a way to determine if it is a 4wd indicator switch as opposed to a VSS?

Obd1