My 2004 rev3 250... My fan will not kick in??

I have tried bypassing the thermostat by connecting a piece of wire between the thermostat terminals and reconnecting the wires to the terminals but the fan does not work. I have tried wiring the fan directly to 12v supply and it spins great? I am now confused - any suggestions?????

When you by pass the thermostat, you just wire it together. Is that what you did? You have to have power going to the fan.

Edited July 10, 201412 yr by lineaway

This reply might help, but not sure if the Evo 4T is a similar wiring loom?

http://www.trialscentral.com/forums/topic/50684-evo300-4t-fan-wont-run-help-needed-to-diagnose/

good chance the rectifier has gone

If the fan feels like it is trembling when the bike is hot, it is getting AC voltage. I think zeorrev3rev4 has the right answer.

From what I have read, I am leaning towards the rectifier.

1. the bypass made no difference - the fan still did not run!

2. direct voltage - the fun run excellent

So I am thinking either rectifier or a loose wire somewhere. I am going to have to do some investigating, maybe remove the radiator to expose the wiring?

Try removing frame side vents and plastic in front of fuel filler to gane access

You already know the fan runs with DC applied to the fan.

If you can use a volt meter, test for voltage at the fan using AC (alternating current) and DC (direct current) scales. It should be DC. Of course, the bike should be at temp so the thermo switch is on.

If you are not familiar with a volt meter, you could also simply connect a 12 volt light bulb in place of the fan. If it lights, you have power. The bulb will light with either AC or DC.

If DC, the fan should work. If AC, the fan will not work. The rectifier is what converts AC to DC power. So, if you find AC power, replace the rectifier and you should be back riding.

That's really helpful. I'm working away but when I get back I will try the volt meter to see if there is power and to see if it is AC or DC - I guess it should be reading about 12v - Right?

possibly 12 to 14 maybe a little less but no more

Yes, 12-14 volts DC