If this one doesn't help you, not sure what will:
http://www.njfboa.org/forums/showthread.php?t=17456
Fan switch (not to be confused with coolant temerture sensor) locations that work: side of RH head or t-stat housing.
A manual swtich is not a good setup as it requires your constant attention. And you'd still need a relay to use one. Just because you are on the ground side does not mean you can use low amp stuff, unless you mean for the trigger circuit and not the fan power circuit.
What kind of car is this (year/engine)? Are they factory fans?