i have led 18 jumped to a free pin (x13) and when the coolant reaches fan on temp, the fan light in MT pulses. No fan turn on.

Also the output voltage on x13 is only ~2 volts, normal?

Could LED 18 not be supplying enough power?

Or is this a software problem?

A post on www.msefi.com wasn't responed to about this question.

The fan output pulls to ground. Use a relay and connect the ground to the MegaSquirt output.

By looking at it, you should be able to remove the LED, and use the negative hole of LED 18, for the fan relay's negative terminal, and then just connect the relay's positive terminal to 12volts, and that should work. The resistor and small transistor needed to drive a relay, are already there, so this should work. There is a positive voltage signal from the processor, goes through the input resistor, which switches a ground, on and off, using the 2n222 transistor. That transistor is what will switch ground to your 12 volt relay. Make sense?

The diagram is at the bottom of the page. Notice on the MS board by each LED, you will see that 1k resistor, and 2n2222 transistor already there on the board.

http://megasquirt.sourceforge.net/extra/outputs.htm

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Just an update to this which might sound stupid - the car has to be on in order for MS to want to turn on the fans I guess.

The fan light pulses only when the ignition is turned on and the fan is set to go on, but the engine is not running.

I think the pulsing is a software problem now. If the car is not actually running, then the fan is never turned on.

ha, fan control works nicely now.