Badmunkie's wiring diagram for a fan switch HERE
; I thought there was one other but I can't locate it.
Fans in general:
Originally Posted by 2003 640a Manual
Coolant is circulated by a water pump located in the engine. When the
engine is cold the cooling liquid circulates only through the cylinder and the
cylinder head. After the engine has reached its operating temperature (about
70°C, 158°F), the thermostat opens and the cooling liquid is also pumped
through both aluminum radiators.
Air blowing in through the radiators cools the cooling liquid. The slower the
speed of the motorcycle, the less the cooling liquid is cooled down. Dirty
radiator fins also reduce the cooling efficiency.
If little or no air blows through the radiators, for example when riding
through slow traffic or waiting at traffic lights, the coolant temperature will
rise. If the coolant temperature rises to 85° C (185°F), the fan 1 on the left
radiator will switch on. This fan will provide additional air circulation through
the radiator thereby preventing the cooling system from overheating.
! CAUTION !
The red cooling liquid temperature warning light 2 will begin to light up, if
the cooling liquid temperature reaches approx. 110°C and henceforth has
exceeded its normal operating temperature.
– riding slowly with a large load at a higher air temperature:
If possible increase your running speed, so that more air can blow
through the radiators. Should the warning light still be on off after 300
meters, stop immediately, switch off the engine and look for other possi-ble
– Too little cooling liquid in the system:
Let the engine cool down, and check the system for leakage’s. Also
examine the cooling liquid level CAUTION SCALDING HAZARD! Do not
drive on, until there is sufficient liquid in the cooling system. Go to your
nearest KTM garage and get it seen to. If you drive with the cooling
liquid temperature warning light on, you will cause even more damages
to the engine.
– The cooling fan on the left cooler is not working:
The cooling fan must be running, when the cooling liquid temperature is
110°C and the ignition is on. If the fan is not working, and there
appears to be sufficient cooling liquid, the only thing you can do is to
drive on to your nearest KTM garage at the least possible engine load.
IF POSSIBLE, ALWAYS CHECK LEVEL OF COOLING LIQUID WHEN ENGINE IS COLD. IF YOU HAVE TO OPEN THE RADIATOR CAP WHEN ENGINE IS HOT, USE A RAG TO COVER THE CAP AND OPEN SLOWLY TO RELEASE PRESSURE.
A mixture of 60% antifreezer and 40% water is used as cooling liquid.
How-ever, the anti-freeze protection must be at least -25° C (-13° F). Aside
from antifreezing protection, this mixture also provides great corrosion pro-tection which is why it must not be replaced by pure water.
! CAUTION !
FOR THE COOLING SYSTEM, USE ONLY HIGH-GRADE ANTIFREEZER (MOTOREX ANTI-FREEZE). USING LOWERGRADE ANTIFREEZE AGENTS, CAN CAUSE CORROSION AND COOLANT FOAMING.
Pressure induced by heating of the cooling liquid in the cooling system is
controlled by a valve in the radiator cap 3 ; a water temperature rising up to
120° C (248° F) is admissible, without fear of problems.
So the easiest way to check the fan is to let the idiot light come on so you know for sure you are in the temp range where the fan MUST be on. It is supposed to come on much earlier, so try this:
1) let the bike idle in the driveway until the light comes on
2) did the fan kick in much earlier?
3) when the light comes on hit the kill switch but leave the bike on
4) is the fan on?
5) last try, use a bit of wire to bypass the thermostat as mentioned below.
PS - did you check your coolant level?
Or you can use the troubleshooting method (mentioned above):
Originally Posted by KTM troubleshooting (from manual)
Check if fan operates properly. To do this, start the engine,
then bypass the connections to the thermoswitch (bottom
right radiator), contact a KTM dealer
IMO coolant display legend on page 10 of the english section of the 2003 640a manual. Too bad they didn't translate it into oil temps...