There are two.
The oxygen sensors are in the exhaust pipes on most models.
Both oxygen sensors are in the exhaust pipe, one under the front of the engine, one roughly under the passenger seat are.
Four
would like to know where the speedometer sensors are on a 1999 villager
How do you change the thermostat in 1999 Mercury Villager
Yes.
There are two oxygen sensors, one in the exhaust near the engine, one in the exhaust pipe after the second converter, roughly under the passenger seat on OBD-II vehicles.
According to the 1999 Mercury Villager Owner Guide : ( 20.0 US. gallons )
In the engine.
No, no room.
134-A
Usually the come in pairs. So 4 seems most likley.