On a 1991 Miata, the battery is in the trunk. It is probably the same on the 1990.
trunk right side.......
The battery is a Mt-MX5. This is a Interstate battery part#. fits 1990-2008 Mazda Miata. Go to interstatebattiers.com to find a dealer near you.
is it under seat
http://www.batterymart.com/p-12v-mazda-miata-battery.html this should help
In the trunk, passenger side
No...not really
fuel pump is in the tank
probably located in the trunk on the passenger side, under the rug. hope this helps.
Battery in Miata's located in the trunk, just open the trunk unbolt the clams and unplug the vent lines, then get an new one and replace it, reconnect every thing and there you go. For more stuff visit www.MX5unleashed.com Have great Miata day!
The battery in located in the trunk, and the positive terminal is the one that is slightly larger and labeled with a + sign.
The best OEM-style battery for a Mazda Miata is the WestCo battery, made specifically for the car. They are of compact size and sealed, since they are located in the trunk. Note that all of the Miata sealed batteries are have small hoses connected on the _ and - sides of the battery. This allows any battery fumes to be ventilated out of the car. An aftermarket sealed battery MAY have these small ports in a different location. You'll just need to go to your local Autoparts store to purchase an extra 1-2' so you can replace the old tubing. Should cost no more than a few dollars. View the related links below for WestCo. This answer is applicable for 1990-2005 Mazda Miatas.
Follow the top radiator hose as it connects to the front of the engine. The thermostat is located in that housing.