:: Fitting a Fan Override Switch ::

Ever been sat in a traffic jam, watching the engine temperature rise, becoming more worried and wishing you'd changed that radiator sooner; or worse still had the coolant flow from the expansion bottle?

If you're in a traffic jam and getting overheated you can always put the interior heater on full hot and sit there roasting, it will help lower the engine temperature...but not the occupants of the car!

By fitting an override switch for the second stage (fast) fan, this little project allows you to assist with engine cooling, as and when required. As this is fitted to a turbocharged Q4 I also use it as part of the cooling down period before switching off the engine...a very useful modification!

If you have any queries about this technical article or wish to submit your own article please email technical@alfa155.co.uk

First...remove the negative battery lead!

While you're under the bonnet look down by the radiator. The red wire exiting the fan switch is what we'll be looking for, but inside the cabin!

Note: the second stage fan is only fitted to aircon equipped cars. This project was for a 2.0 16v Q4 and may differ to other 155s.

Remove the lower dash to reveal the auxilliary fuse box.

The red circles show the location of one screw to the left and two underneath.

Remove the screws and pull the dash to remove, be careful with the area covered by the circle to the right.

This is what I was greeted with, a real mess created by thoughtless previous owners and dodgy alarm fitters!!!

The relays were all in the wrong places and cut wires had insulation tape hanging from them!

So I had to sort them out....

This is what they should look like, we're after number 6 on the right.

Make sure it's the right one and not like mine, with relays just stuffed back in randomly. As you can see in the picture, it's a relay under the top bank of fuses and should have the following wires going to it:

WHT = white
LTB-RED = light blue and red
RED = red (x2)
BLK = black (x2)

The wiring diagram shows everything in more detail...click the picture to see a larger version!

Locate the red wire I've marked with a cross. I used a mulitmeter to test the circuit and make sure it was the wire for the fan.

Work out where you're splicing in and placing the switch, cut enough wire to reach the fusebox (durr!).

Solder on your red switch wire, use heat shrink to cover the join after.

Fix an earth wire to any local earth.

Drill a suitable hole for the switch in your preferred location...make sure the material won't be too thick. I nearly fell foul of this on the dash and had to firmly push the switch in to get the lock ring on the back.

Connect negative to earth.
Connect positive to the load (fan).

Reconnect the battery, head down and......flick the switch! The fan should come on without the ignition being live.

I don't know what rating the switch should be so I bought a large 30A rocker switch with tell-tale illumination as I wanted it to remind me to switch the fan off!

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