ESP systems use a number of sensors to detect the state of the car. Many of these sensors are dual or even triple purpose. For example the ESP system will sense each wheels speed using the ABS sensors on each wheel, and the speedo may well use the signal to display speed (so you see, triple use of sensors, add traction control for a fourth).

The ESP will have wheel speed sensing (probably using ABS sensors), steering angle sensing (with a sensor on the steering column usually) and yaw sensing using an accelerometer (which you are refering to as an esp sensor). It may also have vehicle attitude sensing from height sensors on the suspension on either one pair or all four wheels (my Saab uses the latter I believe).

You will need all sensors to be working and properly positioned for the ESP to function correctly. Without this the ESP might not work at all or may cut in when it shouldn't (which could be dangerous).

I have no idea where the accelerometer would go on your vehicle, but you should find out from a reliable source. Don't guess.