Where is the shift solenoid on 1999 dodge ram van 1500 3.9lt 6cyl?

The shift solenoid on a 1999 Dodge Ram Van 1500 with a 3.9L 6-cylinder engine is inside the transmission. It's not an externally accessible component like a sensor on the engine. You'll need to remove the transmission pan to access it. There are typically multiple shift solenoids.

You should not attempt this repair yourself unless you have significant experience working on automatic transmissions. It's a complex job requiring specialized tools and knowledge. Incorrect installation or handling can cause further damage to the transmission. It's best to take your van to a qualified transmission specialist or mechanic.