You must change the Transmission Fluid as you do it or the oil will leak out the hole the sensor goes in. Its held in by one 10mm bolt on the passenger side of the transmission, next to the ladder frame.
Drain the fluid, unbolt it, pry it out with a screwdriver, reconnect the new one, bolt it in, and fill the fluid, 2.1 qts i believe.
On a 1991 Mazda Miata, the s-sensor, also known as the speed sensor, is typically located on the transmission. It is mounted on the rear of the transmission case, near the output shaft. This sensor is responsible for sending vehicle speed information to the engine control unit and the speedometer. To access it, you may need to lift the vehicle and remove any necessary underbody covers.
The 2008 Mazda MX-5-Miata has a 5-speed manual.
The 2011 Mazda MX-5-Miata has a 5-speed manual.
The 2006 Mazda MX-5-Miata has a 5-speed manual.
The 2012 Mazda MX-5-Miata has a 5-speed manual.
The 2003 Mazda MX-5-Miata has a 5-speed manual.
The 2009 Mazda MX-5-Miata has a 5-speed manual.
The 2005 Mazda MX-5-Miata has a 5-speed manual.
The 2014 Mazda MX-5-Miata has a 5-speed manual.
The 2007 Mazda MX-5-Miata has a 5-speed manual.
The 2002 Mazda MX-5-Miata has a 5-speed manual.
The 2004 Mazda MX-5-Miata has a 5-speed manual.