How do mechanical speedo birds and maro's tell the ecm they're moving? What kind of sensor converts the cable speed to something ecm can understand? Pictures?

 

Mounted on the back of the speedometer is an infrared LED and an photo-transistor (in a small black plastic housing). This picks up the reflection from a small bar spinning inside of the speedometer and sends the signal to a small buffer box. This box has two outputs, one for the ECM and the other for the cruise control (which may or may not get used).

The small box is typically lime green and is mounted on/in the cluster.

RBob.

 

Or yellow.

 

Thanks a lot. That helps a ton.