how does the speedometer work?
 

mine went out and i'm going to try a few things that people on here have recommended. but i would like to know where it gets its reading from.

i know in my integra there is a vss in the tranny that has a cable in it that goes to the back of the cluster.

how does it work on the fd?

I believe it works a little like this:

A sensor (probably a Hall type to sense rotation) in the transmission is connected through the emission harness (X-14) and ends up in the instrument cluster. From there, a signal wire goes out to the ECU and cruise control units. The signal wire is likely to be PWM, but I have to put my oscilloscope on it to know for sure.

The car drives down the road, magic elves see how fast it's going, then they all push really hard and the needle goes up.

Actually, there's a speedometer sensor in the transmission. A gear on the output shaft of the transmission turns a gear on the sensor, the sensor turns it into a pulse that goes to the speedometer. It also feeds the ECU and the cruise control brain.

If you have a PowerFC, see if it will show the speed there. If not, it may be something with the sensor or wiring. If it does work, your speedo may be dying, not an uncommon problem.

Dale