Help 2001 Dakota

The harness is used just because of a redesign issue.
The pressure transducer is separate from the Hi/Lo cut off switch. The Hi/Lo switch is on the filter drier. the transducer is in the line. you are going to need a tester that can read in mil-volts. A DRBIII or a really good diagnostic scanner would be useful.
However, you could have a PCM simply not not supplying current. That could be a bad PCM. But, I've sold 54 transducers (that P/N) under warranty according to my history. The system doesn't track customer pay.