Does anyone know if this GPS speedo sender will work on a 91 speedo?
http://www.intellitronix.com/gps-sender.html

 

I use a GPS speedo in my 69 Fastback, works great. You need to find out what the signal is that your speedo uses. It appears that this unit will work with all the common signals. However your speedo needs to be a programmable. After market programmable speedos are available.

 

Our electronic VSS normally generates a 4000 pulses-per-mile signal. The speedometer-buffer-box (on TBI) or the ECM (on TPI) splits that signal to go to cruise control and the speedometer in the instrument cluster and at the same time it scales it down to 2000 pulses-per-mile.

So that specific GPS sender will work with your car if you plug it into the yellow and purple wires instead of the VSS.