Just below the passenger side door, along the outside edge of the bottom of your Miata, you'll find a seam where the sheet metal meets and has been welded together. Upon careful examination along the length of that seam, you'll find at least two small spots where the sheets of metal flair apart wide enough for coat hanger wire to slip inside. These holes are meant to drain the water that can collect in the body of your Miata after a hard rain. They can easily become clogged with dirt. To clear them, straighten out a coat hanger and gently slide one end into the hole about three inches to clear the obstruction. If water is currently sloshing around in the body, it should immediately begin to stream out.
On my 1990 Miata I have to bend down and look under the passenger dash area close to the floor board and you will see a rubber tubing that has come loose, usually from somebody putting feet to far up and knocking it loose. Just reconnect it
Behind the passenger side seat back, mounted on the rear interior compartment wall. It is under the carpet, near the floor.
In the trunk, passenger side
The AC relay on a 2001 Mazda Miata is under the hood. It is in the fuse box on the passenger side of the engine compartment.
The computer is on a passenger site under the floor board (the very front one that is angled ) inside of the car On this page http://mx5unleashed.com/tech/megasquirt-pnp.html you can see how they take out the computer in the step 2
Leakage in weatherstripping
The horn is right in front of the radiator, on the passenger side on the 2000 Miata. You can see the bracket holding the horn, just to the left of center next to the hood locking mechanism.
Yes, in the steering wheel. Later models will have passenger-side airbags.
The ECU is situated under the carpet of the feet of the passenger. It is protected behind a metal plate.
In the engine compartment, in the service box on the passenger fender.
probably located in the trunk on the passenger side, under the rug. hope this helps.
The 2000 Mazda Miata O2 sensor bank 1 is located on the firewall in the engine compartment. The sensor can be found on the passenger side of the firewall.