that is the oxygen sensor on the exhause manifold.
in the tank
The Toyota mr2
by the oil dip stick
behind the dashboard on the passengers side
under the hood behind the spare tire.
The O2 sensor is located on the downpipe of the MR2, although you were not specific to which MR2 generation/model you are referring to. Most are located there. The downpipe will be bolted to the exhaust manifold, which is bolted to the side of the motor closest to the firewall.
If you are wondering where it is located, it is under the hood, underneath the spare tire.
The battery is behind the spare tire, under the bonnet.
Should be located in the removable housing at the engine end of the upper radiator hose
Its connected to the Fuel Pump inside of the gas tank
how to fix speedometer for Toyota mr2
Under The spare tire in the front of the car next to the battery