The speed sensor on my Villager is on top of the transmission near the starter. If you look down at the starter while standing on the driver's side of the engine, the speed sensor should be to your right, down on top of the transmission housing about a foot or two toward the rear of the vehicle from the starter. It will have a wire going from it to the firewall right about where the instrument panel is located. Note: The starter is under the area of the throttle.
The speed sensor is not expensive and is easy to replace.
on my 1999 ford mercury villager its on top of transmission under the van
You don't as it does not have a cable. You replace the speed sensor instead.
remove and reinstall
In a 1998 Mercury Villager, the mass air flow sensor is located in the air intake tube. The air intake tube goes from the air box to the intake.
on the transmission
O2 sensors are always located on the exhaust system.
A speed sensor on a 1998 Mercury Tracer is located on the transmission housing of the vehicle. It is placed on top in a secure location to safely measure the speed the transaxle spins.
i asked the question how would i know the answer
In the dashboard behind the small grill to the right of the steering column.
It should be the same.
You need to determine if it's the speedometer itself that's faulty, or the vehicle speed sensor. If the speedometer is faulty, you'll need to replace the instrument cluster.