How does Dakota Digital get their speed reference signal? I hope it's not from a sensor in the speedometer cable.
There are a few ways
If vehicle doesn't have a rear axle ABS sensor you can install a 2 or 4 magnet clamp on the transmission end of the drive shaft, and install a sensor to read the passing of each magnet to get a speed signal, which you calibrate using Dakota SGI-100BT
(add-on cruise control kits used this method, prior to VSS being more common)
And you can also get a speedometer cable drive motor, if dash uses/needs a cable drive, its a 12v electric motor that spins the stock speedo cable, it's used with VSS or the SGI-100BT to get the correct rotation speed
This is used all the time on older vehicles when owners want the look of stock dash but the convenience/reliability of newer drivetrains which never had speedo cable hook ups