Where is shift solenoid on a 1994 ford e250 econoline?

The shift solenoid on a 1994 Ford E250 Econoline is inside the transmission. There isn't a single, easily accessible external shift solenoid like you might find on some other vehicles. To access it, you'll need to remove the transmission, or at least the transmission valve body.

This is a job best left to a transmission specialist or someone with significant experience working on automatic transmissions. It's not a simple task. The location and specific type of solenoid will also depend slightly on the exact type of transmission in your van (e.g., E4OD, 4R100). You should consult a repair manual specific to your van's transmission for detailed instructions and diagrams.