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Radiator Fan Override Switch (The Easy Way)

Send me a PM with your email address and I'll send you the full size images.

Oh, and 2 1/2 years now since I posted this write-up and this mod is still working without a hiccup...
 
I think I came across a small problem, does the relay have to have the diode in it? I have the dei 610t relay, the only one I could find locally...
Second, but not a problem- or maybe it is. How to have the ability to turn on when the key is out? (constant power without draining the battery?

thanks!
Btw, I'm standing in front of my XJ with wires, relay and tools... a quick answer would be greatly appreciated ;)
 
I never got around to testing this without the diode. I'm not sure what the effect would be. I'm guessing maybe a check engine light would be the extent of the problems, if any. Give it a shot and report back. If there is a problem, replacing the relay is easy once everything is wired up.

As for being able to use the fan with the key out, you'd just use a constant hot power source in place of the ST-RUN connection. You could take it straight from the battery (use an in-line fuse of course) or you could track down a constant hot that is already fused (the cigar lighter/12v power outlet seems to be a popular spot) and tap into that.

To clarify, it is the factory relay that would need the constant hot in place of the ST-RUN, not the new relay you installed. The new relay doesn't actually control the fan, it just allows the PCM to control the fan after you cut and splice the factory wiring. Not sure what the wire color is or where the easiest place to tap into it would be. I'd have to do some digging in the wiring diagrams. Do you really need to take the key out? Couldn't you just shut the engine off and leave the key in the run position instead?
 
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I have a constant hot right from the battery and it does not work when the key is out. I think it is due to the fact that the pcm does not have power when the key is out.
 
100_8811.jpg

FyrFytr! Awesome thread and everyone else who contributed thx! My '91 is apparently simple to wire - I suppose I'll just drop the relay coil ground off a switch.

I have to say though, your wiring is top notch, though I'm tempted to ship you a soldering iron and some heat shrink to get rid of that crimp on splice! :)

Found this older Fan troubleshooting page that had some helpful info also
http://www.lunghd.com/Tech_Articles/Cooling/Electric_Fan_Diagnosis.htm
 
x e rider. I know this is crazy, but I was re-wiring a scout 800 and a friend that has way more experience than me said never solder in the engine bay use crimp connectors. I did some searching and there are a few post that say crimp not solder. I always like to ask which do you think is better?

I had 3 solder irons at the time and i had no crimp connectors, now i have two of those too.

Nate
 
x e rider. I know this is crazy, but I was re-wiring a scout 800 and a friend that has way more experience than me said never solder in the engine bay use crimp connectors. I did some searching and there are a few post that say crimp not solder. I always like to ask which do you think is better?

I had 3 solder irons at the time and i had no crimp connectors, now i have two of those too.

Nate

Well if you consider for a moment the anatomy of the crimp tap; it's a blade that slices across the tapping wire and wire "on the run". The tapped wire and the tap in wire only have a slim blade width of contact. Both wires can have a few added strands nicked or scarred by the tap. Sure it may last a Long time, but when they get wet they do corrode pretty fast.

If you cut, restrip, slip on heat shrink, dip into flux and solder, all three wires are rejoined with 100% or more of the full gauge of wire, retaining full current carrying capacity. I would not mind using taps inside the cab for low current control wiring. Also, you can use heat-shrink with glue inside for a submersible connection. Just my two coppers on the subject.

Fyrfytr did such an amazing job everywhere else I just assumed he would have soldered and shrunk that connection - was just a tease really, not taking anything away from his install. I wonder if he found a place to use the Zombie switch yet. ;)
 
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I have to say though, your wiring is top notch, though I'm tempted to ship you a soldering iron and some heat shrink to get rid of that crimp on splice! :)

You may notice there are two soldered and heat shrunk connections floating in the background of that picture... :laugh3:

Honestly though, those T-taps are not my favorite. I used it for two reasons:

One, because I was attempting to figure out which wire was the correct one and I didn't want to start haphazardly cutting into my wiring harness. (You may notice some "bite" marks and electrical tape on a couple other wires.)

Two, my soldering skills aren't the greatest. Especially in such a tight spot like that with the rest of the bundle running next to it. Knowing my luck, I probably would have dropped some hot solder on the bundle and melted through a bunch of insulation.

If it makes you feel any better, I went back and covered the bite marks on the incorrect wires with liquid electrical tape. I then replaced the section of wiring loom I cut out to expose the bundle, and securely taped it all back in place. If my override switch stops working, at least I know where to go looking!


Wiring project in process... T-tap shoved back into the bundle where it came from.
100_8818.jpg



All loomed up and ready to rock!
100_0532.jpg


So far as I can recall, everything else in the engine compartment was crimped, soldered, and then heat shrunk.
 
Oh, and no Zombie switch for me, that was somebody else. I have a Lightning switch! :shocked:

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Oh, and no Zombie switch for me, that was somebody else. I have a Lightning switch! :shocked:

000_0047.jpg

Yea just hassling you bro. Hey when you solder, coat both wires with a little paste flux, then coat the soldering iron with some solder, now just touch the soldering iron to the wires, and it will instantly transfer the solder to your wires and no where else. Pow! Try it and your solder-confidence will jump a notch. ;)

Hmm, Lightning switch? Remind me not to drive in front of you - I don't want to be blasted by your Tesla coil hehe :cheers:
 
I won't solder any connections near a source of vibration - chassis wiring and interior sure, but anything that's past the motor / trans mounts gets a sealant lined heatshrink crimp terminal done with a ratchet or hydro crimper.
 
Yea just hassling you bro. Hey when you solder, coat both wires with a little paste flux, then coat the soldering iron with some solder, now just touch the soldering iron to the wires, and it will instantly transfer the solder to your wires and no where else. Pow! Try it and your solder-confidence will jump a notch. ;)

I'll have to try the paste some time. I'm always relying on the cored wire for my flux and it seems that more often than not... by the time I have enough flux on the wire, I have too much solder on the iron.
 
If you use flux, make sure it's electronics flux, not plumbing/general acid flux - the latter will corrode your wiring to pieces in literally months.
 
As a slight variation on this fan switch idea,

I want to turn the fan ON for about ?5 minutes after I turn off the key. This will blow air thru the engine bay and help the heat soak after turning off the ignition.

Any ideas how to do this?
 
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