when I first mounted mine on my 617, I used a jeg's thermo switch, I tape temp probe to thermstat hose coming out of head. I always use a lower t sat. I did not use a relay which burnt fuse up. Finally used one rated for 50 amps. to be sure.My fan only turned on in stop and go traffic in town.

__________________
1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt