First of all...There is no such thing as a "factory installed" remote start on a 05 van
The remote start was a accessory bought over the counter and added on "dealer installed" if you will.
Assuming that it really is a MOPAR accessory piece and not some cluster that a dealer got aftermarket, the box is the same, simply swapping it to a 04 Dakota isn`t just a plug and play, The entire wiring harness is different as is the ignition switch configuration, If the unit has been installed, the SKIM key interface is a one time use (program) piece and cannot be used on another vehicle...So basicly you`ll need a complete install kit...or in simple terms...everything but the actual control box.

Rick