I got a digital thermometer as a present :-)
There 's 3 meters of cable for the outside sensor. This sensor I want to place in front of the car, somwhere behind the frontbumper.
To get there, I've got to pull the cable trough the dashboard and enginebay to get there.
But what't the best place to pull the cable trough? I don't want to make any extra holes in the car ;-)

 

run it through the firewall...find where a main harness goes through the firewall and work through there...usually there is a rubber boot you have to pull out...or alot of times, depending on how hard it is to get to, I just make a cut in the boot with a box cutter. As far as getting the wire through....use some electrical tape, and tape the end of the cable to a long skinny screw driver, or my personal preference a BIG zip tie. I don't remember where I got them, but you can buy a LARGE zip tie that is really rigid and about 2 1/2 feet long...clip the box end off the zip tie and use what's left to tape to the cable. you can fish that thing through alot of tight areas. It's stiff enough to push through alot, and flexible enough to bend around corners and such. Another thing that works well is a long flexible dipstick...cut the ring off the end and use what's left to feed the cable.

 

Same principle, while helping a guy install a switch for his fans on an FD, I used a wire coat hanger. Bend a small loop on the end, it pushes past the rubber boot, tie the wire on, pull it through.