cockpit mounted switch to manually turn on rad. fan

I was trying to figure out how to add a switch in the cockpit to turn on my radiator fan when i wanted to, but i am not too good at reading circuit diagrams...it looks as though (and correct me please if this is not right) the factory rad fan relay (high) becomes grounded when the thermo sensor hits a certain temperature - this completes the circuit and turns the fan on....if the above is true, can i just splice into the relay ground wire, add a switch to this wire, and ground the switch?? then, when i flip the switch, the relay is grounded, and the fan turns on....if the above info isnt right, can someone explain to me a decent way to ovveride the rad fan control with a switch?? Im not interested in having the switch connected directly to the battery in any way though......thanks
dale

 

Dale-I think you read that right. Looks like the "engine coolant temperature switch" grounds the coil of the high-speed relay when the switch sees 102 C, & the relay then provides a path-to-ground for the fan motor. You could confirm (with the key on, probably) by pulling that switch connector & grounding it.I think picture D on page 55-10 (636/934 on the CDrom) locates the switch. Might be easier to test/tap the relay ground wire at the relay itself (picture C). Good luck,Ed
GVR4 #963/2000