Bjorn
I have just fitted an over-ride fan switch to my 1999 +8 , so can show you what I have done. I can't claim any credit for this , my good friend Colin (Spanner Juggler on here) gave me all the design and details I needed.
1 Fit 2 "piggy-back" connectors to the temperature switch.
I appreciate you won't have Halfords in Sweden , but these must be available locally somewhere.
https://www.halfords.com/workshop-t...-connectors-15-amp-semi-insulated-hef3832 Connect 2 cables (15 amp is more than sufficient , you are only carrying the signal voltage which is low current) which are long enough to go from the switch to the dashboard and have some spare just in case. I covered these in electrical trunking to match others in the engine bay and ran them under the intake manifold and plenum assembly through one of the existing bulkhead grommets.
3 Now the decision is how to rig up a switch , the GoMog site recommends a separate switch under the dash but easily accessible. As I don't have any auxiliary spot lights fitted I was able to use the spot light switch. I just disconnected the existing wiring , taped it up, and connected my 2 wires to the same switch.
Let me know if this is not clear and I will endeavour to send you some photos of the finished work.
Once again thanks to Colin for helping me through this project. It is well worthwhile as it enables me to switch on the fan before I come to rest so that I can reduce the temperature , and prevent the normal heat soak that occurs as the engine cools.
Good luck