Thanks Brain, will try that tomorrow and let you know how it fares ;)

So the fan should be setup using output 4 I assume? And not JS3? I was using the settings over from the DIYPNP old MS1 90-93 files as reference for those.

I doubt I wwould havve used js3. I don't think I could even.

By the way, out of sheer curiosity... Does the ECU supply 12V on that line for the relay, or does it just ground the line from the relay? I suppose the thermoswitch being a one wire only probably grounds the wire. Didn't test it.

Just a ground.

Brain, I tested just like you said, and it didn't work... Even though I set everything for outpu 4 (LED18 to Output4, Fan Control in the other panel, and set the temperatures roughly to what you said) but the fan kept on running. I was able to observe that, with LED18 set to Warmup (like it was) the Output4 gave an ON signal on Megatune's dashboard, and with it set to Output4, the Output4 gave an OFF signal. Regardless, the fan kept on running.

Also I noticed it only runs IF the engine is running. I thought it did on ignition, but nope, it's only with the engine revving. On ignition, the fan stays off.

Also, while searching the internet regarding this problem, I found out the previous owner of this ECU was having the same problem on his car, systematically burning out the relay due to over-usage.

Could it be that something inside the ECU is messed up? :(

Should I try and see if it works properly using JS0/X2?

Switched LED18 back to Warmup, and X2/JS0 to Fan Control on the outputs tab.

All fine and dandy :)

Thanks a lot for the help guys!

oh okay great!

This board is modded with VICS, Knock and WB inputs from what the previous owner told me :)

Okay so I'm back with NEW problems regarding this...

After I set the X2/JS0 to Fan Output like I said before, it all worked fine until recently. A new relay got stuck AGAIN! Only this time it was clicking while the car was cold.

I checked the relay wires with a multimeter. Between the main tabs, there's a differential of 12V which, when shunted, turns on the fan. That checks out.

I then checked the relay activation line. It measures a despisable amount of voltage when ignition is on (< 0.05V ), it measures a variable amount of voltage with the engine ON, and when the Fan is finally at the set temperature, it shows 14V as it should.

Now the odd thing is... The values it shows on the voltmeter with the engine running while below fan threshold are odd. They vary between 1-2V on the display, but from the relay clicks I figured the relay is momentarily activated at the same rate as the engine turns. It is as if there was an impulse signal to the relay when the fan is below threshold but the engine is running.

Could this be caused by a bad earth somewhere, a misconfiguration in my MS, or should I be looking into damage inside the MS itself?

Any help would be appreciated as this almost cost me my engine a few days ago when the car overheated badly because of this...

Could it be that, because the fan wasn't meant to be controlled by the ECU, when both the ECU and thermoswitch activate, the fan shuts off? I dunno, I'm completely lost here. I've tried everything I could think of!

no, both just pull the relay to ground, they can work in conjunction.

Radiator Fan Running with ignition off
 

My 91 Miata continues to drain the battery during the night sitting in my garage with the ignition off. I changed out the relay that I thought was the issue and changed the battery as the old one was weak. I walked out a week later to find the Miata fan running full blast with the ignition off. Could the temperature sensor cause this issue with the ignition turned off or does anyone have any other ideas? thanks