I installed my fan switch yesterday and I have a few tech tips I would like to share. First of all it was much easier, at least on my 85', to run the ground wire through the fire wall with the other two wires and attach it to ground in the engine compartment. It requires cutting off the ring terminal to route but it's easy to crimp another back on. The reason I did this was because the frame was not very asscesible on the floor board. They tell you to drill a 5/16" hole right behind where your left foot rests, but there is too much rubber and foam to move out of the way. Also it's much more pleasent working out in the engine compartment rather than being stuck headfirst into a space that was made for your feet to be. It was much easier to route it out through the firewall and connect it near the other wires.


Additional tip:
I pay'd 20.00 including S/H for the harness. You can buy the switch ( center off, 3A250vac ) and diode ( 1N540) at Radio Shack for about $6.00. Buy about 20 feet of black 20 gauge wire also. Solder the diode across positions 1 and 3 on one side (row)of the switch ( the switch has two row's of three positions). Now cut the wire into 3 equal sections and solder a wire to each pin on the same row as the diode and there you have it, your very own home made fan switch for about a cost of $8.00.

 

What does the diode do?

 

I am not really sure to tell the truth. It's conncted between the two wires that are connected to the green and white wire on the fan relay. I think it might be some sort of currrent limiting diode or some other sort of limiting devise to help protect either the switch or the wiring.

 

The diode allows the sw to pull the fan relay control line to ground to energize the fan while preventing a positive voltage spike from getting to the ECM fan control output circuit.

It also prevents the sw from reverse biasing that output circuit (in case the ECM trys to energize the fan while the manual sw is closed) as the diode likely has a voltage drop similar to that of the ECM driver.

 

The purpose of a diode is to allow the current to flow in one direction only. By installing a diode between term. 1 and 3, this will allow the power to go to 1 fan when switched to the terminal that has the diode blocking the current flow to the other, and then when switched to the other terminal would allow current to flow to both 1 and 3 therefore bringing on both fans. I believe this is how they are switching on one, or both fans with one switch.

 

That makes sense :cheers: