Originally Posted by hornetball
Yes, all US Spec Miatas came with the same harness. Uninstalled options result in unpopulated plugs.
They were close, but not identical. For instance, try getting a VSS signal out of a '92 that was made without cruise or an automatic transmission. Exactly one wire is missing from the instrument harness, even though the VSS sensor itself is there. And the worst part is that the wire IS there in the "front" harness (which connects to the ECU, cruise computer, etc), it's only missing from the "instrument" harness. So you think you have the wire when you're hooking up the ECU, but it only goes as far as Common Connector X-17, where the Front harness joins the Instrument harness.
I'm not sure about the later cars, but the 1.6s were filled with fidgity little omissions like that, where a single wire is missing if the car was built without an automatic, or cruise control, or power steering, or ABS, or autonomy from the Queen, etc. And in '93, California cars got their own completely separate set of harnesses, unique in all the world. The early wiring diagrams are full of these little notes:
And so on... Makes no sense to me- it'd be a lot easier to stock a single harness in the factory rather than fifteen different versions of it? But they did. The parts catalog confirms this:
Fifteen different versions of just the front harness alone, just for the '92 model year.
But yeah, everything hornetball said is correct with regard to identifying the connectors. The blue plug was indeed put there by Mazda to power timing lights and other dealer service equipment, since there's no battery under the hood to clip onto.
I confirm the guess about the cruise control actuator.