I am having a problem with my speedometer in a 91 RS, 305, carb and T5. I have tried the drill a hole and use long piece of wire to reset speedo back to zero, worked for a short time now problem is back. I have removed all the junk on passenger firewall, ac, heat etc. basically stripped out all computer junk. Ignition is toggle switch and relay as well as fan, fuel pump and starter. I have repair guide from austins in pdf form, however, does not go into any wiring detail or schematics. Any help would be appreciated.

 

The speedo gear, now an AC generator, is wired into the PCM, then PCM to speedo. for indication.

 

what gear are you talking about? no speedo gear on 91 t5 transmission

 

Get a Haynes manual. Thereis a toothed wheel with a coil;picking up the pulses and inputs to PCM.