Radiator Fan Override Switch (The Easy Way)

[clean4drxj]

Ok, I read about 8 pages and couldn't take it anymore LOL!

I want to wire a fan override in my 96 without CEL issues, I do have AC. What do I need to do?

I've got the dash apart wiring in a new sound system so this would be a good opportunity to put a switch in.

Curious on this as well, I have a 96 also...

 

[hubs97xj]

Mine is still working fine. The PCM doesn't care what the fan itself is doing, so no CELs.

I posted a (IMO) simpler circuit to control the fan, based on CharlesS' idea. Page 3. Easier than it looks.

 

[xjtrailrider]

Mine is still working fine. The PCM doesn't care what the fan itself is doing, so no CELs.

I posted a (IMO) simpler circuit to control the fan, based on CharlesS' idea. Page 3. Easier than it looks.

Yep, I saw your circuit for the 97+, but I have read that the 96 ECU doesn't need that complicated of a circuit to keep from throwing a CEL which surprises me since the 96 is OBD2?

Just looking for a confirmation or a circuit diagram of a 96

 

[hubs97xj]

I think Gradon had posted the how-to for the 96. I know I've seen it in one of the fan threads, but that method didn't work for me (invariably threw a code in some situation), so I wound up using CharlesS' idea, which works great, and should work for any year, since you're basically adding a redundant control for the fan.

 

[kastein]

^ agreed. It is pretty simple, heck the way I added it to my 98 required 1 mini iso relay, a few bits of wire/terminals from a 97+ I pillaged the pdc from at the JY, and about 20 minutes of disassembly/crimping/reassembly. You would only notice if you checked in the pdc and wondered why a non abs jeep had an abs relay.

96 is a funky year for electronics. It won't detect many failures a 97 or later will.

 

[TdiJet]

Awesome thread! I just have one question that I didn't see answered (or asked lol). fyrfytr1717 mentioned about the illuminated switch lighting up every time the fan cycles normally and it's easily remedied. I would love to wire up an LED illumited 5 pin switch to keep the flow of my interior but as this circuit is "all different", anyone have any ideas?

PS: I'll say it now, I know nothing about wiring but I have been diligently working my way into threads to wire things up lol. just had to put that out there.

 

[TdiJet]

haha... in fact I am trying to use the same switch pictured in the first initial post on this thread. I would love for the switch to work in it's intended illumination states.

 

[Jonner]

I usually order mine from Susquehanna Motorspots. Here's a very helpful page on their website in regards to picking out the right type of relay for your needs.

http://www.rallylights.com/hella/Relays.aspx

The HL87104 is the relay w/ diode that I usually use. It can be used NO (Normally Open) or NC (Normally Closed) so it allows for some flexibilty in that regard.

If you want to mount them as seen in my pictures, use them in conjunction with the HL87123 Mini Relay Base w/ terminals.

For a typical relay (such as this fan override project) I would want normally open, correct?

EDIT: I just realized they spell out the part numbers... so I answered my own question.
HL87104 - 12V, AgNi - (4RD 960 388-25)
HL87424 - 12V, AgSnO2 - (4RD 003 520-25)

I'm putting an order together on their website to tackle this in the next few weeks. I'm tempted to order their rally mudflaps too... been eyeing those for months now. This would be for my daily driver with typical overheating issues.

 

[860xj99]

First, I would like to thank you again for all of the info provided in this thread it have been most helpful. I have tried doing it the same way and I am having some issues and no fsm to fall back on. I have the switch on the dash set up for a 12- signal. When I crimped that and the db/pk to the fan relay together to put on terminal 87 of the relay the fan would run with the switch in the off position and shut off in the on position, also when I tried to ground the db/pk to the relay just to check if it would work it didn't but would turn the efan on if i put it to the positive terminal on the batt. Im sure it is something stupid simple that I screwed up but after spending hours on this today I am at my wits end and still have no idea where I went wrong. The thing that is really bothering me is I am usually really good with this type of stuff so its driving me nuts and in tern my fiance also. Any info or direction would be greatly appreciated by the both of us.

 

[fyrfytr1717]

Hard to say without knowing a few more details of your setup. Seeing as it seems to be operating in the opposite manner from which you are expecting (both with and without the switch), I would suspect that you have a couple of your wires switched on the relay. Maybe you are using pin 87a instead of 87? Maybe your relay is normally closed (NC) instead of normally open (NO)?

Regardless of your wiring, grounding the DB/PK wire that leads directly to the factory fan relay should cause the fan to come on.

A few more details or some pictures might help troubleshoot your issue.

 

[860xj99]

The problem I was having was that I didnt have the relay hooked up yet. I just had db/pk to fan relay and new switch put together on one side of a butt connector. I think I am getting closer to fixing the problem tho. I found that with the ignition off if I put a jumper on the db/pk to the fan relay and and ground it I get nothing but if I touch it to the positive side of the batt. the fan comes on. With the ignition on it is the opposite, ground will turn the fan on and power does nothing. This stikes me as odd. Then I took a closer look at my switches with a volt meter it seems that the switched I am using providea -12v source when on but when off they provide +12v. The switch I am trying to use is a dorman rocker switch with a incandecent bulb rather than led so I wouldnt have to pull the switch apart and flip the led leads so the led would work. I guess I will need to find some new switches but I am still puzzled as to why the fan relay works different depending on if the ignition is on or off.

 

[fyrfytr1717]

Well I don't have the answer to all your questions, but I can explain the seemingly odd behavior of your fan relay. The way a relay works is that the internal switch is activated when there is a difference in potential between the two pins. If either side is disconnected, you get nothing. If both sides are grounded, you get nothing. If both sides are fed 12V+, you get nothing.

When your ignition is on, 12V+ is supplied to one side of the relay by the ST-RUN circuit. When you ground the other side, the relay activates and turns the fan on.

When your ignition is off, one side of the relay is presumably being grounded by the unenergized ST-RUN circuit. When you apply 12V+ directly from the battery to the other side, the relay activates and turns the fan on.

The fan doesn't care whether the ignition is on or off as it is connected directly to the battery. Only the fan relay cares.

As for your switch, you're going to have to mess around with it a bit. You can't wire it as suggested by the directions if you want it to supply a ground. If it is a three pin indicating switch being used in a typical configuration... pin 1 is hooked up to the 12V+ source, pin 2 is the output, and pin 3 is hooked up to ground to make the light bulb turn on when activated. You should simply be able to hook up pin 1 to ground, pin 2 to the output, and pin 3 to a 12V+ source to make the light bulb come on. This won't work with a LED switch, but it sounds like you've already figured that out. I'm guessing based upon your voltmeter test results, you have pin 1 and 2 (input/output) reversed.

 

[860xj99]

Thank you for explaining why the relay is acting the way it was that makes perfect sense now. As for the switches I guess I will just pick up a simple on/off toggle without a light. I do have one more question tho and it is a bit off topic so I apologize in advance, I am using the same type switch as a extended idle switch, if that one is doing the same thing and providing +12v when off could that possibly damage the pcm?

 

[fyrfytr1717]

If I'm undertanding you correctly, you are saying that you are using the same Dorman switch for the extended idle mod and fear that it may be feeding 12V+ to the PCM when in the "off" position? If so, that pin on the PCM is intended to be either grounded, or have no connection at all. I can't tell you for sure whether or not supplying it with 12V+ would damage the PCM, but I definitely wouldn't reccommend it.

 

[860xj99]

Thats what I thought thank you for all of your help.

 

[01xjJE]

i tryed this today but i was trying to use a led switch which was very clean looking. how ever it did not work very well. Has any one figured out how to do this using a led switch?

 

[jodybbad]

I knis thread is old as the hills but I have a question maybe someone could help. I have a 98 tj with an aw4 and a xj PCM I am getting the p1491 fault code when I turn my a/c on because I don't have an electric fan. So I drilled a hole in my gray PCM connector for the c-2 pin and installed a connector pin I salvaged from another harness. Now I just have a wire hanging there ready to be connected to something. What is the PCM looking for could I just use a diode or will I need to wire a relay in?

 

[jodybbad]

alright it quit raining so i got outside and wired a light bulb to the gray c2 connector. Now dont get a check engine light with a/c on or off and the bulb lights up when the a/c pump kicks on. My new question is what do i use to simulate a light bulb. the c2 connector is a ground btw.

 

[jeeperjohn]

alright it quit raining so i got outside and wired a light bulb to the gray c2 connector. Now dont get a check engine light with a/c on or off and the bulb lights up when the a/c pump kicks on. My new question is what do i use to simulate a light bulb. the c2 connector is a ground btw.

Just use a LED and cover it with tape.

 

[jodybbad]

Yeah maybe so. I haven't tried an led yet to see if that would work. I am thinking about a resistor also.I just don't know what size to get.