i want to install a manual fan switch. i am putting in a lower thermastat and want to be able to cut the fan on early too. my desired circuit is one that will allow me to manually turn on the fan at any time with a single pull single through switch, and also have a backup automatic temp sensor set lower than factory(i forget what temp, but i know that a 160 stat is almost pointless unless you change the fan cut on temp). i guess what i need help with is understanding the circuit that the temp sensor and fan cut on switch is in. a schematic or something. thanks for any help

 

I went to my fan relay (mine attached to the radiator bracket) and grounded out the wire that lead to the temperature switch.
Easy way....unhook the relay....notice the 2 little wires in the middle of the connector.....measure voltage.....which ever on has none....ground that wire to switch on the fan.

I used a insulated alligator clip and a short piece of 16 gauge wire. I only manually control the fan when doing cool downs at the track. I will add a SPST switch later.

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86 T/A 5.0 A4 & 2.77 gear
15.62 @ 86 mph
93 Civic 1.6L
13.5 @ 100 mph

 

ok cool. i can do that. so if i replaced your aligator clip and wire with a spst would the fan automatically come on when the switch is open and the temp sensor reaches the temperature that makes it conduct. or would i always manually have to turn my fan on?

 

With SPST open, fan acts normally. Al the factory switch does is ground the circuit. The SPST does the same thing.

Another little trick I plan later......
Fan will come on after brake pedal is depressed more than 15 seconds. Like if you were sitting in traffic. That way once cruising fan would be off.

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86 T/A 5.0 A4 & 2.77 gear
15.62 @ 86 mph
93 Civic 1.6L
13.5 @ 100 mph

 

ok, i have an 87 z28 wiht lg4. the fan realy would be where? would it be on the drivers side near the cowl? so which wire do i need to ground? where does it come from in the circuit and where does it go(normally)? i checked the schematic in the hays manual and the fan switch circuit comes from a linkable fuse(red or brown wire i think) to the relay, then out the relay(red wire i think) to the fan switch and out to ground.

does the spst need to short out the realy?