SPD signal ECU

[firehawk]

The actual sensor which generates the signal for the ECU is behind the combination meter, as this is where the speedo cable comes to. On some newer cars, the sensor is directly on the gearbox and the speedo is driven electrically.

Anyway, I found some info on where the SPD signal is being used in addition to the 180km/h limiter. The ECU uses it to keep the idle speed control system disabled when it detects that the car is moving, even if the throttle is closed (IDL signal is low). So if the SPD signal is missing, every time you let off the throttle, the car will think that it's idling stationary and use the idle VSV to adjust idle speed.

However, since you've removed the idle-up VSV from your engine, this shouldn't cause any problems. If you'd still want to generate the SPD signal yourself, a simple reed switch which connects the SPD pin to ground four times per wheel rotation will do the trick.