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Thermo Fan Timed Run On

Anyone who owns a rotary knows that cooling them down is a big priority. This modification helps the cooling process.
I've chosen to install a push button that will call the electric cooling fan on for a period of 5 minutes. This push button can be perssed at any time to operate the fan, either while driving or with the car stopped and ignition off.


Jaycar Kit KC5379
UB3 enclosure to suit
Micro push button
10 amp cable
40 amp cable
Fuse holder
Crimp terminals
Cable ties
Insulation tape, etc




Usual toolbox including:
Soldering iron
Electric drill





So if you go to the trouble of actually doing this modification, the first thing is to assemble the kit. Here it is here, and I'll leave a big resolution of it for reference. Note the timer setting at 300 seconds (30 seconds x 10 via the multiplier). Also note the position of the other 2 jumpers.


So we got the kit assembled but first thing we need is to give it something to control.
The logic is to install a relay to switch the thermo fan. First some technical bits to put your mind at rest:
- The thermo fan is fused at 40 amps. I'd suggest that current draw is only applicable at full load, ie 150 kmph turning into the air flow. Stationery, probably more like 5 amps. However I'm wiring it up to handle full load but not eveybody may find this nesessary.
- The OEM thermo fan relay operates in a "normally closed" condition to provide fail safe operation. Installing this modification will have no impact on normal operation.
- Powering up the OEM normally closed relay while the ignition is off DOES NOT feed power back to the ignition circuit.


So first thing is to tap off the existing fan supply under the fuse box with some 40 amp cable.

Its shown here with the soldering done but not yet taped.






A good spot for the new relay is under the diagnostic box, cable tied to the loom.
Connect the cable installed in the previous step to one side of the relay contact.
Run a negative wire from a good chassis point to one side of the coil (10 amp wire will do).
Using the 40 amp wire, pick up a good power supply - the battery is close by and can be easily tapped off. Run this cable through a fuse and to the other side of the new relay contact.

By using a temporary piece of cable, you can now apply 12 volts to the other side of the relay coil for test purposes. The thermo fan should operate.

  Find a convenient location to mount the timer switch. I put it behind the TV screen.      
  Mount the push button and run the wires back to the timer.    
  Pick up a 12 volt and negative supply and run these to the timer. The load on this supply is very low as it's only operating a couple of relays so a power supply that feeds the radio is more than sufficient. Install a 5 amp fuse in this wire.      
  Run a 10 amp wire from the new relay under the bonnet to the timer.      
  Make all the necessary connections at the timer, cable tie and neaten all wiring, and your ready to go. Just push the button.    
  I've set the timer initially to 5 minutes. This can be adjusted at a later date to extend the time if needed.