Cooling fan stays on
 

Is it supposed to be on during warmup ? It's always on, unless the key is switched off or I unplug the thermoswitch (new, same as old) or unplug the fan.

1992 (long nose)

Is there any sign of a previous owner messing with wiring, or any modifications to the car?

From the factory, there are 3 ways the fan can come on. If the thermoswitch activates, if a certain pin is jumped in the diagnostics port, or the ECU actuates is. I'm not sure why there is the thermoswitch if there is a trigger wire going to the ECU but maybe someone else knows. Check continuity over the thermoswitch when it's unplugged and at ambient temperature (a condition where the switch would be cold). Check the diag connector for jumps. Check for weird splices or switches that may have been installed.

Only time I had to fight fans coming on before coolant was at temp when setting up a megasquirt was due to AC wiring being jacked up.

Wiring looks factory. Previous owner put 4-1 headers and advanced timing. No jumps at diag or anywhere. Do you know where I can buy the connector for the thermoswitch? Forgot to mention that broke. Wire is on and not touching anything, but it's not insulated = bad ? I'll check the continuity, thought it was that for a while just been lazy.

I'm running into the same thing on my '91. Pre-turbo, after the recent rebuild, I'd notice the fan kick on as soon as the key switch was in the "on" position. I've noticed the top of the harness' connector has some wires showing through the insulation that has cracked / stretched/ broken out. My guess is that the wiring to the connector, right at the top is shot- there isn't much for strain relief and after 27 years... I've contacted Miata Blake to see if he has any spare he'd cut off for me. If you have time, junk yard sort of item might be also be an alternative.

Another thought about the harness plug that I may explore is using a later model switch. Yet, I don't know if it opens "off" ground? Looks like all one would have to do is wire one end to ground and the other to the harness. I might try this out in the future as a used harness pigtail is only going to have the same issue eventually, just a matter of time.

Anyone know if the NA8 (or later) fan thermo switch in the coolant neck opens "off" ground? I guess another way of phrasing is that continuity to ground is broken.

Wait, you're saying your thermoswitch is disconnected, and you're wondering why the fans are working funny?

It's connected.

Oh, I see. Misread that. Get all of your connectors at Ballenger. These guys are awesome, and they support the community a lot https://www.bmotorsports.com/shop/mazda_miata.php

Back to my point about AC. Do you have AC? Did the car have AC at one point? Do you have two fans or one?

Have AC, doesn't make cold air. One fan as of right now, removed the AC fan (passenger side). Driver side fan was always on before and after removing the AC fan.
Cool website, though looks like they don't have it.

Check to see if the AC on button is pressed or even try pulling the AC relay? My gut says it's AC related

Tried unplugging the AC relay if that's the one with a boot over it, fan still on. AC button was off