I have a '97 I purchased several years ago, and had to do an engine change, new engine(5.9 V8) has a single temp sensor, old had a dual temp sensor. How do I make the gauge(Violet/yellow wire and plug) function?

 

You could possibly put some sort of T fitting into the port to allow the use of the two sensors or pickup an earlier model intake manifold that has the provision for the two sensors. Did you keep the intake off the old motor?

Just FYI, the two wire sensor is critical to get it hooked up correctly or the truck won't run it's best. The two wire sensor sends the engine temperature data to the PCM so it can properly calibrate the fuel going into the engine.

 

Best option would be to reinstall the old manifold that already has the provision for two sensors. Next would be drilling and tapping your current intake for the sensor. I wouldn't do the T-fitting thing, as the PCM needs ACCURATE temp info to properly run the engine.