I’m looking at building a custom speedo/tach display built into a custom handlebar clamp, and I have a couple questions. I’m going to be doing this to my stock 1999 Sportster Hugger 883 that is currently residing across the state at my parents for the winter.

After looking at the wiring diagrams supplied by my local Harley dealership, I have identified a couple different signals of interest:

1. The Speed Sensor Output which is connected directly from the Speed Sensor to the Electronic Speedometer (‘W’ through connectors 39 and 65)
2. The Tach Signal which is supplied by the Ignition Module (‘PK’ though connectors 10, 20, and 136)
3. The Speed Signal Out from the Electronic Speedometer which is connected directly to the Turn Signal Module (‘W/GN’ through connectors 20, 30, and 39)

When I talked to the dealership, the service guy told me these signal were either analog, serial, or a CAN bus. However, because it is an older bike, he did not know for sure. I have scoured the internet and service manuals, but cannot find the answer. Obviously, if my bike wasn’t stored for the winter, I could poke around with an oscilloscope and find out.

My questions are:

1. What is the data format of these signals?
2. How is the Speed Signal Out from the Electronic Speedometer to the Turn Signal Module related to the Speed Sensor Output? Are they the same, or has some processing been done to the signal inside the Electronic Speedometer?

Any help with this would be appreciated. I’m an undergrad senior in Electrical Engineering, so if I can just get this figured out, the rest of the project should be no problem. Once I get going, I’ll post updates on the design.

 

The only thing I was able to find so far is this info:

Speed Sensor leads:
R-Red: +12 VDC
W-White: Output signal (square wave)
B-Black: Ground