The easiest thing a person can do to customize their vehicle is with an aftermarket set of wheels and tires. Nothing more says “this is mine” like bolting up a set of “low pros” on dubs, or a set of monster truck tires. In either case, when you alter the diameter of the tire, it will alter the reading of the speedometer – and it needs to be changed back to read proper speed. Enter the Speed Wizard from Merlin Controls.

The Speed Wizard is a necessity for any truck that has larger or smaller than stock diameter tires. Implementation of electronic speedometers occurred around the mid 90’s, when most automakers introduced a whole host of electronic controls (read: OBD II). As a result, correct vehicle speed is now critical to the proper operation of the vehicle – and the Speed Wizard does this by altering the speed signal at the source, done by signal processing technology. The hardware in the Speed Wizard uses the incoming frequency signal (Hz), processes it using a multiplication factor (described later) to output the correct signal to the vehicles engine control module (ECM) and/or powertrain control module (PCM).

One of the best things about this system is the method used to adjust the Speed Wizard isn’t simply a trial and error. With a series of simple mathematical equations (which totally delights the admitted geek in me), you can calculate the amount of change you need even before leaving the driveway. I was able to dial in the proper speed in two tries. It would have taken only one try if factory calibration were more accurate! All this is done while the vehicle is parked, where you can safely make adjustments. This prevents me from having to make any adjustments while barreling down the road in an 8,600 pound lifted truck!

Speed Wizard Highlights:

• Corrects speedometer / odometer readings.
• Eliminates speed signal related reductions in engine performance and fuel economy, as well as related changes in exhaust emissions.
• Infinite adjustability provides precise speed signal calibration within 1%
• Simple four-wire hookup.
• Includes complete instructions and adjustment equations.
• Can be recalibrated infinitely for future tire size or gear ratio changes.
• Works on most Ford vehicles equipped with an electronic speedometer.

The Installation

Tools needed:

Wire crimpers
Wire strippers
8mm socket with extension
Soldering iron

The Speed Wizard comes with only the parts that you will actually need, and there are NOT that many parts. That goes to show the simplicity of the product. Included is the Speed Wizard control unit itself with a four wire lead, heat shrink, crimp connectors, zip ties, and Velcro adhesive.



The best place to tap into the factory wiring is from behind the dashboard. Removal is quite easy. The entire dash cover is held on with clips. Start pulling at the dash and the clips will release themselves – no tools needed. (Be sure to unplug all the switches as you pull them out – headlight, radio, cigarette lighter, and radio.) When the gauge cluster is exposed, four 8 mm screws (indicated by the red arrows) will remove the gauge cluster.



There will be three connectors behind the dash. Look for the gray 12-pin connector (C220b), indicated by the red arrow. Pin location 3, a gray with black tracer 18 gauge is the wire the Speed Wizard needs to be spliced into. It is the VSS+ wire.



See the wiring diagram of the connector: