Yeah, the manifold is the sensor you want to tap. I'd recommend a Helms manual to help you find the right wire. You'd hafta find out some specs on the sensor to see what the output swing is. However, if the signal thats important to the ECU is the current from the sensor, don't fuck with it unless you have someone there who knows exactly what will happen electrically.

I dunno if its useless or not. You need to do some serious research on the sensor and the normal operating ranges and what the ECU is meant to see when your car is on.