Radiator Fan Override Switch (The Easy Way)

[spinaldex]

Based on what I've read, I thought the electric fan in an XJ is based around the ground wire not being connected until its passed through by the thermostat control. Couldn't you just splice in to that wire right at the fan, and then run a toggle to a switch which is grounded? On = grounded and the fan runs, off = still running under normal control from the truck.

??

[Veeb0rg]

No, splicing at the fan would do no good. The ground that's not connected is at the relay in the PDU. Connecting to the ground wire for the relay with a toggle to ground will allow the functioning as you said. Newer 97+ jeep don't like it however and may throw a CEL light, the older ones don't care.

[spinaldex]

Has anyone done this a high amp toggle switch to apply power directly to the blue wire going to the fan on a 00-01 to see if does a CEL? I bought a relay and the darn thing isn't labeled so I have zero clue which one is 87, 87a, 30, etc. But that got me thinking why not just run a toggle to simplify the whole thing?

[Miller88]

If I'm reading it right, yes, a few people have. It causes the check engine light to come on.

I just went to the junkyard and grabbed a fog light relay out of another XJ to use for this. It's labeled, was $.50 and is more than up to the task of activating the real fan relay.

[MrSimon]

I just used the write-up on the first page on my 2000. It was easy and works great. Thanks for the write up!!!

I took me about half an hour to do the whole thing.

[fyrfytr1717]

Glad to see people are still finding this thread useful, 6 years later! The override is still working as intended on my XJ...

[gradon]

Today I was diagnosing my 2nd e-fan not working and it turned out to be the fuse instead of the relays. Switch still works and no cels. I rec this thread on occasion. Thanks again.

[MrSimon]

I have a wiring question.

Since I am feeding the new fan relay a GROUND signal from the in-cab switch, I don't have a 12v source going to the switch (standard five pin rocker switch).

I'd like to wire the switch up so it illuminates when I turn on the headlights like other switches. My problem is that the pin where I usually feed the switch a 12v signal is currently used to feed the ground signal.

How do I get the switch to light up?

[mechbullxj]

Originally Posted by hubs97xj

(apologies to fyrfytr for cluttering up the thread)
Okay, poking around with the meter, doing some googling. The light blue wire isn't ground, it's power. Ground is black, and unswitched. The relay in the PDC, when energized, puts 12V on the blue wire, fan runs. Taking an educated guess here, but is this how you actually wired it up, Charles? (and sure enough, the PCM doesn't monitor the fan, just the control ckt)



Switch off, stock power wire connected to 87a (NC) contact, wire from fan connected to 30, fan runs only when PDC energizes.
Switch on, battery power on 87, fan on 30, stock power wire held open, fan runs constantly.

Have I got it right?

This is how you'd wire your aux. fan, it uses a SPST switch. I've a SPST switch that has three terminals to power the circuit. It's a Daystar KU80011. No.7 is the ground for the lamp, No.3 is power out, and 2 is power in. Using a switch like this the lamp lights when the fan is turned on. Having a switch light when using the cars lights you would have to have the switch spliced into the headlamp switch directly. Not sure how to wire with your particular 5 terminal switch.

[fyrfytr1717]

I really wish the above referenced wiring diagram had never been posted in this thread, it really did clutter it up and causes confusion as it is in conflict with the idea/intent of this thread.

That being said, you can still make your switch light up with the rest of your instrument panel so long as your switch provides for that option. It works fine with my Carling switch. The main light illuminates when the fan turns on/off, and the secondary light turns on/dims with the rest of my instrument panel. Can you provide a pin out diagram of your switch?

One issue you may have however is dependent on the type of bulbs in the switch. Incandescent bulbs don't care if the + and - are switched so you can just ground the positive pin and apply the dimmer signal to the negative pin. If you have LEDs in the switch on the other hand, you may be out of luck as LEDs don't let current flow through backwards.

[MrSimon]

Here is the switch I'm using.

I have #6 hooked to the dash lights and #7 grounded. This works great for the lower light on the switch. It comes on with the dash lights and dims nicely. No problems there.

I am feeding a ground signal to #2 and #3 goes to the fan relay I installed.

The switch works the fan exactly as it should with no problems.

If I ground #8, then the top (larger) light on the switch is on all the time and GOES OUT when I turn the switch on. It's like the fan relay is back feeding a 12v signal to the switch when the the switch is in the off position.

Any thoughts? I'd like the top light to come on with the fan and go off with the fan.

[mechbullxj]

Try connecting #2 to your relay and #3 to the fuse. At your own risk.

[fyrfytr1717]

mechbull... please stop. Guessing at electrical and offering it up as advice only causes confusion and quite possibly damage/fire.

MrSimon, connect the dots... According to your diagram, there are two individual circuits in your switch. The circles with the "X" in the middle are your bulbs and need (+) on one side and (-) on the other in order for those electrons to flow through your bulbs.

1. The dash light circuit begins with (-) on pin 7, passes through the bulb, and ends with (+) on pin 6. You currently have that wired according to the diagram.

2. The indicator light circuit in our application is reversed. We need to apply (-) to pin 2 so that pin 3 receives a ground signal when the switch is activated. Since pin 2 is (-) and passes this (-) on to pin 3 when the switch is activated, pin 8 needs to be (+) in order to complete the circuit.

Two possible issues. First, as I mentioned previously, if the switch uses an LED for the indicator this will not work as current only flows through them one direction. Second, if (despite what the drawing shows) pin 7 & 8 are actually a common (shared) ground for both lights, this will not work as desired. Do a continuity test between pin 7 & 8 to find out.

[mechbullxj]

Yes, don't guess when doing electrical work. Should Mr. Simon switch #2 and #3 on the switch, a fuse could be blown, or circuit breaker tripped. If it did happen to ruin the switch he'd be able to start over. Buy a new switch, one that doesn't offer up a confusing wiring scheme. 4 amps to your relay. At your own risk.

[MrSimon]

Originally Posted by fyrfytr1717

mechbull... please stop. Guessing at electrical and offering it up as advice only causes confusion and quite possibly damage/fire.

MrSimon, connect the dots... According to your diagram, there are two individual circuits in your switch. The circles with the "X" in the middle are your bulbs and need (+) on one side and (-) on the other in order for those electrons to flow through your bulbs.

1. The dash light circuit begins with (-) on pin 7, passes through the bulb, and ends with (+) on pin 6. You currently have that wired according to the diagram.

2. The indicator light circuit in our application is reversed. We need to apply (-) to pin 2 so that pin 3 receives a ground signal when the switch is activated. Since pin 2 is (-) and passes this (-) on to pin 3 when the switch is activated, pin 8 needs to be (+) in order to complete the circuit.

Two possible issues. First, as I mentioned previously, if the switch uses an LED for the indicator this will not work as current only flows through them one direction. Second, if (despite what the drawing shows) pin 7 & 8 are actually a common (shared) ground for both lights, this will not work as desired. Do a continuity test between pin 7 & 8 to find out.

For the indicator light circuit, if the light is coming on when the switch is in the off position, there must be a + signal coming from somewhere, right? And it can only be coming from the new fan relay that I installed according to the original instructions in this thread. Is that normal?

If it is normal, and I feed a + signal to the #8 pin, won't I have two + signals coming in from different sides of the same circuit?