What part controls speedometer output to VSS output.? I have 12v into speedo. But on red wire to vss..only 11.6v. ?

 

Sensors usually have power supplied from a ECM regulated source. Commonly 5v, 8v, or 12v. The VSS will take the regulated input voltage and output (usually) a square wave that the speedo interprets.

In some cases the VSS signal will output to either the ECM or other computer before passing to the gauge. It may pass thru unchanged or it may be converted into a different signal type.

The VSS itself is just a reed switch. A normal voltmeter won't be able to diagnose it.

Usually there is a functional description of each system in the Service Manual.

 

I have this 2001 fxdwg, and on HD drawing, going into the speed. I have 12vdc, coming out of this speedo, 3 wires, red, blk, WHT,.. According to drawing, the red wire feeling the Vss should be 12vdc?, but as I tested it.. Only getting 11.60 vdc... I need someone with the HD electrical manual that shows the power requirements to these items.. 😁 I guess it's possible the speedometer is bad.. Before I buy another... Thanks anyone.. Lol

 

I'd be surprised if that's outside the specified limits.

What are your symptoms?