GM DRAC/VSSB Calibration
If you are carbed, this is what you need to drive an electric speedo. They are easy to find in 92-95 Chevy/GMC full size trucks, its a white box mounted under the ECM. Make sure you take the pigtail as well.
Easy to wire it too. Just de-pin wires you won't be using and braid together the VSS sensor wires to prevent interference. Connect 12V+ switched thru a 2A fuse, ground, and the C15 VSS output to the speedometer input. Calibrate the box using the method above, and done. Way cheaper ($5 if the junkyard even charges you) and guaranteed to work correctly vs the universal Dakota Digital method for $89.
