I had some problems with my 2000 sporty and found that if has diagnostic codes built in. I turned the key on while holding the button on the back of the speedo and it gave me the code for the sensor. Changed that and it sovled the problem.
Speedometer Diagnostic Codes
The following is taken from the HD Factory manual, 2000 edition:
SPEEDOMETER - DIAGNOSTICS
XLH Models have a speedometer with self-diagnostic capabilities.
GENERAL
The reset switch is used to change the odometer display between mileage and trip values and to reset the trip odometer. It is also used to identify the speedometer calibration and to enter the diagnostic mode, clear diagnostic codes and exit diagnostic mode.
DIAGNOSTIC MODE
The Diagnostic Mode is entered by turning the ignition from OFF to ON while holding the reset switch in. The normal power-up sequence will occur before entering the diagnostic mode. Diagnostic codes set during this power-up sequence will be stored as well.
Important Note: Be sure no diagnostic codes are indicated before reset is held in for more than 5 seconds or diagnostic information will be lost.
When in diagnostic mode the odometer will display the first diagnostic code. When the trip switch is pressed again the next code will be shown. If the trip switch is pressed for more than 5 seconds at any time while in the diagnostic mode, the diagnostic code displayed will be erased.
There are 7 different diagnostic codes available. They are as follows:
d01 - Speed sensor power output shorted low
d02 - Speed sensor power output shorted high or open
d03 - Not Used
d04 - Not Used
d05 - Speed sensor return shorted high
d06 - Speed sensor return shorted low
d07 - Not Used
d08 - Speedometer power over voltage
d09 - Speed output shorted high
d10 - Speed output shorted low or open
CAL XX - Speedometer application calibration number:
14 = Domestic
15 = HDI
When in the diagnostic mode, all codes are displayed in sequence from d01 to d10.
As a code appears in the display (for instance d02), it will read "d02Set" if set or "d02CLr" if clear.
The diagnostic mode is exited either by turning ignition from ON to OFF to ON again without depressing the reset switch or if a speed signal greater than 5 MPH is detected.
Diagnostics cannot be performed if system voltage is less than 9 VDC or greater than 16 VDC. The only exception is d08 which is set when system voltage is greater than 16 VDC.
After all the diagnostic codes are displayed, the speedometer calibration number is displayed (CAL 14 for example).