i know this slp switch thing but i think it's quite expensive... ~65 $ + shipping for such an easy function
@garry
your link seems to be very useful. thank you very much. i will try this out when the weather here in germany becomes warmer and better
i hope that i understand everything correctly and the whole thing works fine when i'm ready. the comments below the description are very useful, too
EDIT:
did it today! i found out an easier way to install a fan control switch: for 3.4 (and maybe earlierer lt1) just search for the green cable that comes from the ecm on the passenger side and goes to a bigger connector. it is the one that is at the "J" port. then simply switch it to ground and the fan turns on.
later years have a blue and a green cable for high and low speed. just look at the passenger sides connectors.
very easy mod. works fine