90 and 94 Diagnostic Module

Location (on a US miata)

It's located on the driver side fender This is on a 1990 miata.   Click for even closer view.

Electrical Connections (for a 1990 and 1994 miata)

Not all of the positions have terminals.There are 11 terminals in my 1990 and 1994 miatas. This list is not not inclusive. Miatas after 1994 may have a different layout. Mazda makes a special electrical tool that plugs into this socket to allow technicians to access the enginecomputer, airbag, and test vearios relays. The home mechanic can make use of some of the signals in this connector.

    Signal Name What I Think it does*







Used by a Mazda test tool. It apparently can drive an LED or lamp and acts like the check engine light in the dashboard for reading computer error codes on the 90-94. Do not connect to either +12 or ground, Non-US cars may not have a check engine lamp. In that case, a light bulb or LED between FEN and B+ will serve the same function.
  2. MEN Don't know what this does. Mess with it at your own risk..





Used for timing engine and for reading out Error Codes. Connect to a GND pin to activate. On a 94, if you press the accelerator with this pin grounded, the radiator fan will run





This is 12 volts. Used by Mazda test tool. Never ever ground this pin or there will probably be a fire in your wiring. Better yet, never connect anything to it.
  5. GND Ground. There are two grounds.





Looks like the same wire as air bag warning light in the dash. Probably used by a Mazda tool to read the air bag controller,
  7. -IG Tachometer signal. Goes to your tach on a 90 and a 94. Do not ground or connect to +12.
  8. GND Ground. Goes to same place as the other ground..





Test Radiator Fan. Ground this pin and cooling fan should run. Used to test cooling fan relay and cooling fan.








For testing fuel pump. Ground this pin and fuel pump relay closes so you can testif the fuel pump or fuel pump relay work. It's a safety hazard if you drive around like this because it defeats Mazda's fuel pump shutoff.






Test Air Bag? Goes to the horn switch in the steering wheel. If you ground this wire, the horn goes off, but it's also indirectly connected to the airbag. My opinion? Don't touch it..

*Disclaimer: Not a certifed auto mechanic. Not a Mazda technician. The information on this page is my own interpretation and may be flat-ass wrong. Use at your own discretion.