vehicle speed sensor on 1991 Volvo 740

were is the vehicle speed sensor for a 91 volvo 740 and whats the difference between the front and back sensors

Asked by for the 1991 Volvo 740
What issue are trying to fix? ABS or speedometer?
Speedo uses the rear differential sensor and the ABS uses the rear differential sensor and front wheel speed sensors.
My abs light is on and my speedometer goes in and out
I would check the ABS codes, and check that rear differential sensor and wiring. If yo look at the back of the differential you'll see the sensor with 2 wires going to it.