Trying to figure out why my speedometer doesn't work.1988 Fiero GT Getrag 5 speed. 4.9 Caddy carburated and single wire HEI distributor. for this to work does it need the origional ECU? It appears to be wired but I just got this car and it is kind of crude on the wiring in the engine compartment.
The Vehicle Speed Sensor (VSS) has two wires, purple and yellow. The purple wire goes to C203 R. The yellow wire goes to C203 G.
The C203 connector is in the console, below where the stock ECU would mount. The connector is translucent white and has two black plugs connected to it.
If no chassis side wiring mods were made, this should be all you need to get the speedometer working, as the ECU is not needed to make the speedo work.
You can also do a quick check of the VSS my pulling it off the transmission, connecting a multimeter set to AC and spinning the end the gear is on. The meter should read a small amount of voltage. If it stays on zero the VSS is bad. They sometimes do go bad, my VSS went bad. In my case the seals in the VSS went bad and somehow got transmission fluid into it. If your VSS is good, then check the wiring from the VSS to the dash. If the wiring is good, then you might need to pull the dash cluster and inspect the printed circuit boards to see if it has gone bad.
Another problem can be a missing gear on the VSS. The VSS on a 5 speed points down and the gear is just pushed on the shaft. If you pull the VSS and there isn't a plastic gear on the end of the shaft, that is your problem.
As everyone else said, VSS connects to a Yellow and a Purple wire. They run to C203. There they go up to the connector on the dash. And last is the speedo.
