Jump to content

Elec Fan Switch Mod


Recommended Posts

I have a KC light relay with switch and fuse already in the cab. My electric Fan Is not working like I think it should or when it should. Ive already disconnected the harness and stuck the the Ground and positive jumper from the relay in the harness and checked to see if the relay would operate it which it does. Now my question is if I hard wire the Fan to the relay and leave the harness disconnected will this negatively affect operation of other things? I know it connects to the relay on the fender which tells it to kick on from the radiator sensor and ac motor. But will leaving the connection at the fan open affect anything else? I live in Hawaii and believe the engines temp should have that fan running all the time. Ive got idiot lights until the new cluster comes in the mail. Ive taken temps at the intake manifold with a digital meat thermometer have had readings above 210 while idling up in the garage. New T stat along with a new pressure bottle and full flush in a week when the parts come in. Ive read the fans are possessed and read alot about people hooking up a switch in the cab. Couldent find anything describing the process.

Link to comment
Share on other sites

  • Replies 51
  • Created
  • Last Reply

Top Posters In This Topic

I'm not clear which relay you plan to use and where you plan to unplug the existing harness. If I were going to do what you want to do, I would skip the KC relay, unplug the connector between the radiator temp sensor (driver's side tank) and the fan relay, and just connect the switch to those two wires.

 

Or not even unplug anything. Use Scotch quick taps to splice into the two wires coming off the radiator tank, then you can let it run normally or use the switch to override if/when you feel the need.

Link to comment
Share on other sites

I was planning on cutting the wires behind the fan harness on the fan side. I was going to use a existing switch and relay which is already wired to the front of the truck and to the cab for the non existent KC lights.

Or not even unplug anything. Use Scotch quick taps to splice into the two wires coming off the radiator tank, then you can let it run normally or use the switch to override if/when you feel the need.

Wanted to do it this way :clapping: To the sensor? not to the fan itself? Wouldent that just energize the sensor? I'm a plumber not a mechanic or electrician. Slowly getting more familiar with automotive electrical with your guys help. :help:

Link to comment
Share on other sites

I was planning on cutting the wires behind the fan harness on the fan side. I was going to use a existing switch and relay which is already wired to the front of the truck and to the cab for the non existent KC lights.

I think I understand that your intention is to have the fan run all the time, but if you do it this way you will have no option. You will HAVE to run it all the time, or else always control it manually. In cooler weather, if you turn off the fan switch it cannot come on automatically with the a/c because you will have bypassed the control circuit.

 

 

Wanted to do it this way :clapping: To the sensor? not to the fan itself? Wouldent that just energize the sensor? I'm a plumber not a mechanic or electrician. Slowly getting more familiar with automotive electrical with your guys help. :help:

You already have a fan relay and the circuit to control it based on either radiator temperature or a/c operation. IMHO it makes no sense to cut out the relay that's intended to run the fan and then use a relay that's NOT untended to control the fan.

 

The sensor in the radiator is nothing but an on/off switch that's actuated by temperature. You can't "energize" a sensor. You would disconnect the wires from the back of the switch, tap onto the two wires coming off the radiator sensor, and run two new wires directly to your switch. That leaves the entire OEM fan control system intact, and allows you to use your toggle switch as a manual override.

Link to comment
Share on other sites

The sensor in the radiator is nothing but an on/off switch that's actuated by temperature. You can't "energize" a sensor. You would disconnect the wires from the back of the switch, tap onto the two wires coming off the radiator sensor, and run two new wires directly to your switch. That leaves the entire OEM fan control system intact, and allows you to use your toggle switch as a manual override.

 

I had changed out the radiator with a 91+ rad to do my OPEN system swap. Didn't have a bung for the switch/sensor so I needed a way to turn the fan on due to temperature if I'm towing/in traffic/crawling or just super hot temps. This way I never really bypassed the relay, it's still part of the loop. I just keep an eye on the temp or use it a kind of a pre-emptive measure when I know the Jeep is about to be under more load. It really works pretty well. I can also turn the fan on the Jeep is off, just to cool things down under the hood.

Link to comment
Share on other sites

Whoa.....

 

 

You did make sure that you protected your wiring from fan voltage backfeeding into whatever switch you used??

 

I did the same thing your pictures look like they show on an old XJ... The fan kicked in on its own and fried the switch and wiring in the cab. Lots of really awful smelling smoke is how I was rewarded. I redid it like the link ParadiseMJ posted... works great...

Link to comment
Share on other sites

You guys make this far more difficult than it is.

 

None the wiring for the fan should inter the cab.

If you want to control the fan with a switch inside the cab, obviously the wiring has to enter the cab.

 

The difference between doing as Craig Houghtaling did and the way I suggested is that doing it Craig's way allows you to run the fan when the engine is off. Doing it the way I suggested won't run the fan if the engine is off.

Link to comment
Share on other sites

You guys make this far more difficult than it is.

 

None the wiring for the fan should inter the cab.

If you want to control the fan with a switch inside the cab, obviously the wiring has to enter the cab.

 

The difference between doing as Craig Houghtaling did and the way I suggested is that doing it Craig's way allows you to run the fan when the engine is off. Doing it the way I suggested won't run the fan if the engine is off.

 

 

 

I've done it both ways.

 

If you want to run the fan manually all you have to do is run the trigger wire (what I consider the 'low volt' wire to the cab and for that matter you have simply run the common through the switch and not even bring the hot side in.

 

I had no advantage to running the fan after shutdown...........if the cooling system is functioning correctly there is no purpose for it.

 

 

For simplicity-

 

Relay mounted to fender wall near battery.

Hot to fan from relay.

Fused link to relay from battery.

Trigger from any ignition source wire to relay. Wire at loom on fender.

Ground from temp switch at thermo housing (to complete circuit when temp is reached) wire to neg of fan.

Or if two wire thermo switch at rad tank.......one wire to ground and one to ground and one wire to neg of fan.

 

 

No wire need be longer than 24" and except for the trigger wire no wire should be less than 12g.

Link to comment
Share on other sites

Thats what i was scared about in the first place. I got so many conflicting responses I just did it. I have the separate KC light relay connected directly into the fan circuit. Should I change it? The separate relay is fused.

If it works, don't change it. But the KC relay is redundant, because you now have a relay controlling the "trigger" function of the OEM fan relay.

 

@lsmurphy, everything in an MJ is 12 volts, so your characterization of the "trigger" wire as "low voltage" is way off base. What I said stands: If you want to control the fan with a switch, you MUST run wiring into the cab. (Unless you want to go high tech and create a wireless remote to actuate the fan relay.)

Link to comment
Share on other sites

Thats what i was scared about in the first place. I got so many conflicting responses I just did it. I have the separate KC light relay connected directly into the fan circuit. Should I change it? The separate relay is fused.

If it works, don't change it. But the KC relay is redundant, because you now have a relay controlling the "trigger" function of the OEM fan relay.

 

@lsmurphy, everything in an MJ is 12 volts, so your characterization of the "trigger" wire as "low voltage" is way off base. What I said stands: If you want to control the fan with a switch, you MUST run wiring into the cab. (Unless you want to go high tech and create a wireless remote to actuate the fan relay.)

 

 

 

 

I understand that.

 

But you are not running the heat or amp draw through 6.5' of wire or through the weakness of the in-dash switch.

 

There is no discernible draw on the 'trigger' wire.......you are only activating the relay.

Link to comment
Share on other sites

Eagle is right; it makes more sense to use the existing fan relay wiring rather than adding another relay. Since I run two electric fans, and the main cooling fan is where the mechanical fan used to be, I wanted a means to manually control the aux fan from the dash in case my main fan went belly-up. I wanted to retain the factory controls of the aux fan (ON when A/C is on, and/or when the temp reaches 225* or so). So I simply tapped into the coil side of the stock fan relay and wired the new dash switch to apply a ground signal to the coil and trigger the fan as in the wiring diagram.

 

This diagram is for the HOs. The Renix aux fan uses switched 12VDC rather than a ground to the fan relay coil, but the wiring principal is the same. Use your new dash switch to apply a signal (Ground or 12VDC) to the coil side of the existing fan relay.

 

Link to comment
Share on other sites

My second relay is tapped directly into the red wire coming directly from the fan not from the sensor. That way the relays act independently from eachother I believe. Since the KC relay is just sitting there all hooked up with no KC light to operate I figured It was alot easier then trying dig through the rat nest of relays on my fender. Its wired up for 4 switches in the cab that until now had no function. So as long as its not going to fry anything if it does magically decide to turn itself on one day I'm going to just leave it alone and admire how when I hit the switch it turns on engine on or off. It blows a nice stream of cool air into the engine compartment. Its like under hood air conditioning while wrenching on hot days. jamminz.gif

Link to comment
Share on other sites

I understand that.

 

But you are not running the heat or amp draw through 6.5' of wire or through the weakness of the in-dash switch.

 

There is no discernible draw on the 'trigger' wire.......you are only activating the relay.

Of course -- that's why the relay is there. But the "trigger" signal is still 12 volts.

Link to comment
Share on other sites

I understand that.

 

But you are not running the heat or amp draw through 6.5' of wire or through the weakness of the in-dash switch.

 

There is no discernible draw on the 'trigger' wire.......you are only activating the relay.

Of course -- that's why the relay is there. But the "trigger" signal is still 12 volts.

 

OK, I should have said the 'low current' not low volt.

Link to comment
Share on other sites

  • 3 years later...

Eagle is right; it makes more sense to use the existing fan relay wiring rather than adding another relay. Since I run two electric fans, and the main cooling fan is where the mechanical fan used to be, I wanted a means to manually control the aux fan from the dash in case my main fan went belly-up. I wanted to retain the factory controls of the aux fan (ON when A/C is on, and/or when the temp reaches 225* or so). So I simply tapped into the coil side of the stock fan relay and wired the new dash switch to apply a ground signal to the coil and trigger the fan as in the wiring diagram.

 

This diagram is for the HOs. The Renix aux fan uses switched 12VDC rather than a ground to the fan relay coil, but the wiring principal is the same. Use your new dash switch to apply a signal (Ground or 12VDC) to the coil side of the existing fan relay.

 

 

Hi Hornbrod,

 

Sorry for digging up old stuff.

 

So I tried this tonight:

 

Checked fan are input wires and it spins; great.

 

Located the BLU/PNK wire from my wiring harness (near the driver side/clutch MC) and grounded it like I think you are saying with the above diagram.

 

Grounded the BLU/PNK wire...

 

The relay clicked but the AUX Fan did not turn on.

 

I then started poking around and ended up blowing the AUX fan fuse :/

 

My Question I guess is for clarification on the above diagram....in relation to a common Bosch relay (85/86/87/30 pins) how do your 1/2/4/5 pins correlate? I was pretty sure it is 85 = 4, 30 = 2, 86 = 5 and 87 = 1, but that didn't work out for me...

 

All I have to do is ground the BLU/PNK wire, right....?

 

I have a 1992 MJ 4.0L stock under the hood.

 

Thanks!

Link to comment
Share on other sites

The relay pin numbers on my diagram are numbered according to the FSM wiring diagram, and that's how the pins are numbered in the PDC aux fan relay socket. Pins 1 and 5 are the relay coil, corresponding to Bosch relay pins 85 & 86; pins 2 & 4 are the load contacts corresponding to Bosch relay pins 30 and 87. If your relay clicks (energizes) when you ground the BLU/PNK wire, then the circuit is working as it should. Verify this by unplugging the aux fan and apply the ground to the BLU/PNK while monitoring the + lead to the aux fan connector. You should see 12V when the relay clicks.

 

Don't ever test a new circuit with the load (fan) plugged in - use your meter to test the voltage, not the load so if something's wrong you don't blow a fuse.

 

Automotive-Bosch-Cube-Relay-Pin-Outs.png

Link to comment
Share on other sites

Thanks so much!

 

This may be a silly question, but must the truck be running? And not only the key in the run position?

 

I definitely heard the relay click...and the fan was plugged in...but now that I think about it, the engine must have not been running...

 

Oh and my reverse lights are not working now...:/ Are the two issues related somehow by chance...?

 

Thanks again!

Link to comment
Share on other sites

Thanks so much!

 

This may be a silly question, but must the truck be running?  YES  And not only the key in the run position?

 

I definitely heard the relay click...and the fan was plugged in...but now that I think about it, the engine must have not been running...

 

Oh and my reverse lights are not working now...:/ Are the two issues related somehow by chance...?  NO

 

Thanks again!

 

This aux fan wiring mod has been done by many with no problems on the HO models. Did your aux fan work as it should (comes on with the A/C and/or if the coolant temp goes above ~230* degrees or so) before you started the wiring?

Link to comment
Share on other sites

Thanks for the reply.

 

The PO must have put a 4-prong relay in the AUX fan location. I'm thinking from Hornbrod's replies that it must be a 5-prong. I will replace the blown 15A aux fan fuse tonight and put the proper relay in that spot. Turns out also the 4-prong relay is pinned differently...so my issues are probably stemming from that:)

 

I never had the aux fan working; everything is stock under the hood pretty much, and the A/C is hooked up but not charged. I'm thinking either remove it, charge it and see if it works or turn it into onboard air...

 

I noticed the temp crawling high, but not close enough to the red range for me to worry. I would stick the heater on and it would climb down. Now that I want to wheel a bit more, I'd like to have the option on turning it on/off where necessary. This mod seems perfect for what I want to accomplish.

 

Thanks for your replies, and I'll be trying this out in the next couple days.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share


×
×
  • Create New...