What I want is a single switch that will allow me to (1) have a manual "constant on" fan override AND (2) have a fan disable (for deep water). I finally decided to do a little research and found a wiring diagram that I think does what I want AND has a couple of built in features that I didn’t think about. I’ve also been chatting with a member here to make sure this will work. If he doesn’t mind the credit, I’ll edit the post and include his name, lol. If you guys see something wrong, speak up. I haven’t tried to wire it up yet.
Anyway, this first diagram is the basic diagram from the other site. Basically, using a SPDT switch, you tap into the fan 12v wire between the stock fan relay and the fan. Current supplied to the wire, via the switch (position 1), runs to the fan…bypassing the stock relay which is controlled by the temp sensor and ECU. Thus the "constant on override".
The "extra" gizmo is the "shutoff relay". If I understand correctly, this relay is by default in the closed position…which allows the current to run through it (whether coming from the stock setup OR the override setup) and operate the fan. If you put the switch in position 2, it energizes the coil in the "shutoff relay", which opens the circuit, and kills power to the fan. Thus, the disable function. It also energizes an indicator light to let you know that your fan is totally disabled, and if for some reason, the relay fails, it’ll default closed to keep the stock system intact.
The next diagram I came up with today as I looked at the layout. I was concerned about the full load of the fan being pulled through the switch when using the override function. So I added another relay between the switch and stock fan wire. This relay would basically be triggered by the switch and pull the current from a 12v source such as the battery, fuse block, etc. Everything else would work as above.
With the switch in the "off" position, everything should work as normal, through the ECU, as if none of this was attached.
What I’m not sure about is if I should wire any diodes into the system to prevent back feed into either the stock relay, or override relay.
Like I said, I’m looking for opinions on this setup before I try to wire it up. I know a lot of you guys are considerably more skilled in electronics than I am.
