Are you saying that you are unsure where it is on the car, or unsure why u would need one?
It is built into the FD on the gearbox. The output shaft drives the diff round, and the two drive shafts fir into either side of it.
Normally with big power front wheel drive if you nail it out of a bend, the wheels will spin and the front will drift out. With the diff if you feel it starting to drift, plant the power and it draws the front back into line (to an extent).
M.C.