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Old January 11th, 2011, 14:44
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Mudderoy Mudderoy is offline
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Join Date: Feb 2008
Location: Katy, Texas
Posts: 1,894
Re: Radiator Fan Override Switch (The Easy Way)

Originally Posted by fyrfytr1717 View Post
Hey Mudderoy, been awhile since I've seen you post up here. I imagine XJTalk takes up a majority of your forum time these days. I appreciate your taking the time to provide some feedback. Anyways, I was reading your version of my write up that you linked to in your post and had a couple questions.

I saw that your work around was hooking the relay coil up directly to the battery instead of using the DB/WT wire that I recommended. That should work too as you just need a 12V+ source to make the relay work, but my reason for using the DB/WT is that it is an ignition switched 12V+ source. If you have it hooked up to the battery instead, you could potentially forget to turn the override switch off and cause your battery to drain when you shut the vehicle off. Granted a relay coil doesn't draw much power, but the fact is that the relay coil would remain energized and it would be a small power draw that would eventually leave you with a dead battery. If you don't want to use the DB/WT wire, I'd suggest finding another source of ignition switched power or setting up an ignition switched bus bar for accessories that you don't want to accidentally leave on when the ignition is shut off.

Second, you recommended installing a 10 amp fuse between the switch and the ground. Why? A relay only draws about 0.16 amps so a 10 amp fuse would do very little for you. Additionally placing the fuse where you suggested offers no protection to anything except the short piece of wire connecting the fuse to the ground. You are however correct that you should install a fuse when using your suggestion of hooking the relay up directly to the battery, but it should be as close to the battery as possibly and only needs to be a 1 amp fuse to protect the relay and associated wiring. Using the DB/WT wire for relay power takes advantage of the fact that the DB/WT wire is already a fused circuit.

Again, thanks for the feedback. Maybe I'm just missing something and you can clarify for me?
Hey thanks for the reply. I purposely didn't mention my site as I didn't want to be doing FREE advertising on another Jeep XJ site.

The site pretty much runs itself, so I've been spending more time setting up for a live ustream show and podcast.

This is a great mod and it really helped me get off my a$$ and get her done. I had a problem with the check engine light initially and was really happy when I finally got that resolved.

I didn't want to hook the relay up to the 12 volts directly but having it connected to a 12volt source that was there and not there seemed to be telling the ECM that there was a problem, therefore the check engine light would come on. After a few weeks of staring at that light and thinking about what my OBD II scanner was telling me it dawned on me I needed a constant 12 volt source going to the ECM. I can only assume that I am correct since providing that constant source resolved the check engine light issue.

As for the 10 amp fuse, well since I have running the ground wire to the switch when I bypass the relay and turn the fan on, grounding it, I am running the full current of the electric fan through that ground wire and the switch.

I probably need to install another relay and let all the current be there under the hood. I was concerned about the wire running to my over head switch box becoming light bulb filament and glowing a bright white just prior to the headliner fire.

I'm doing all this by memory. I need to go back and look at the diagram and re-read my post.
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