Try this:
http://www.mx5parts.co.uk/advanced_sear ... ic&x=0&y=0
I've just bought one of these on the recomendation of Stuartspel.
"This manual explains the functions and uses of that mysterious black box located near the air filter-the diagnostic connector. The procedures apply equally to most models of Mazda MX5, Miata, and Eunos Roadster. The purpose of this manual is to enable the home mechanic or independent garage to access the self diagnostic facilities of the MX5 which are normally only available to Mazda dealers through the use of their factory provided service tools. Includes a free DIY led probe to get you started!"
I guessed you've worked out that it's the same port as on the F, and that myself and Stu are happy to recommend it!