Radiator Fan Override Switch (The Easy Way)

Project00XJ said:
So.. my problem was that the blue and white wire in my harness showed power in the run position and ground in the off position. With further testing it was not enough to open the relay. I ran a jumper to the 86 post and it worked perfect. No cel. Lol turns out my vehicle has 2 harnesses that run side by side by the hood hinge on the driver side. I figured my wire to the batt was good enough, so when i was about to be done and put the other harness ( which was pulled out of the way) i said what if, well is was. Turns out both harnesses have a blue whit wire and the other one did the job.
Click to expand...

Good for you for working it through Project00XJ! As I had mentioned in my write up, there are at least 2 DB/White wires, 1 DB/Grey wire, and 1 DB/Yellow wire that run through the engine compartment in that general vicinity and could be easily mistaken for the correct wire, especially in less than ideal lighting conditions. Use the wrong one, and this mod doesn't work properly as the other wires are either the wrong voltage or do not turn on and off with the ignition switch. You really need to make sure that you perform a continuity test between the wire you're planning on using and Pin A2 on Connector 1 in the PCM. This ensures you are using the ST-RUN wire, not some other Dark Blue wire.

100_8811.jpg


I just went out and looked at my XJ and low and behold, in the smaller harness running next to the one containing the DB/Pink wire, there is another DB/White wire. I have yet to test it, but you may have just stumbled across another location for an ignition switched wire! In fact, this looks like it may be the wire that is directly connected to A2 on Connector 1 in the PCM. Jeep likes using the DB/White color code for ignition switched power sources in a variety of locations throughout the XJ. Good find!

100_0529.jpg


In reality, the DB/White wire is not some magical wire that is the only way to make this mod work. It just happens to be the closest ignition switched power wire in the area where you need to tap into the DB/Pink wire. You could just as easily tap into any another ignition switched wire, set up an ignition switched bus bar for this and other accessories, or use a constant hot as Mudderoy continues to suggest. As I mentioned last time Mudderoy made this suggestion though, you need to exercise extreme caution with using a constant hot for this mod. If you inadvertently leave the switch on after shutting down your Jeep, the relay will remain energized and slowly kill your battery.

Additionally, I finally got around to buttoning things back up. I took the piece of corrugated loom that I cut off to access the harness and snapped it back into position. I put the tapped and spliced wires resulting from this mod into a smaller piece of loom, and then wrapped everything back up together with electrical tape as the factory likes to do. Doesn't look perfect, but at least it is all secured and protected once again.

100_0532.jpg
 
I don't believe so. However, the good news is that from the write-ups I've stumbled across I seem to recall that the earlier models are actually easier to deal with as they don't throw a CEL when you tap into the fan control circuit. It may have been as easy as wiring up a 12V+ lead from a switch directly to the factory fan relay? Don't take my word for it though, hopefully someone that is familiar with the earlier models can lead you in the right direction.
 
fyrfytr1717 said:
I don't believe so. However, the good news is that from the write-ups I've stumbled across I seem to recall that the earlier models are actually easier to deal with as they don't throw a CEL when you tap into the fan control circuit. It may have been as easy as wiring up a 12V+ lead from a switch directly to the factory fan relay? Don't take my word for it though, hopefully someone that is familiar with the earlier models can lead you in the right direction.
Click to expand...

On my 96 I wired a 12V+ lead directly to the fan plug from a 12V switched relay and was able to manually control the electric fan. Doing this never caused a CEL to come on. Good luck.
 
Mike L said:
On my 96 I wired a 12V+ lead directly to the fan plug from a 12V switched relay and was able to manually control the electric fan. Doing this never caused a CEL to come on. Good luck.
Click to expand...

I was hoping somebody had wired up a fan override on their early model in the same spirit as this thread, controlling the factory fan circuit via a switch as opposed to wiring in an additional circuit to power the fan...

XJRunner said:
on my 87 i run a wire with an inline fuse to a switch than directly to the fan
Click to expand...

And you haven't fried your switch yet? Must be a pretty stout switch to be holding up to powering your fan without use of a relay.
 
fyrfytr1717 said:
I was hoping somebody had wired up a fan override on their early model in the same spirit as this thread, controlling the factory fan circuit via a switch as opposed to wiring in an additional circuit to power the fan...
Click to expand...

thats what i want. i want the fan to work exactly like normal, but be able to turn it on a little early if i feel like it. If i see a big climb, and i know by the time i'm at the top i will be over heating, it would be nice to turn the fan on at the bottom of the hill.
 
Well that ^^^^ was a long, confusing read. From what I gathered, on '95 and earlier models, you can just splice a new wire into the DB/Pink wire, run it to a switch, and then connect the other side of the switch to ground. Much easier.

It was interesting to see my wiring diagram included in that thread as well. I don't frequent JeepForum much. Thanks for the credit MrJCRod, "someone on another forum"... :rolleyes:
 
fyrfytr1717 said:
Well that ^^^^ was a long, confusing read. From what I gathered, on '95 and earlier models, you can just splice a new wire into the DB/Pink wire, run it to a switch, and then connect the other side of the switch to ground. Much easier.
Click to expand...

thats what i gathered. there were also schematics to run a lighted switch, a 3 position switch etc.

hope you don't mind the jeepforum link, i thought it would be helpful to someone who had a pre 96 and stumbled across this. now this covers 91-00
 
FYI - I tried the splice method on pin C2 in my 98 and the CEL came on. I wanted to see if that worked as it was easy to do and no relays needed, but it looks like I will in my application. Thanks.
 
I just finished doing this on my 01 XJ at first it only half worked and I got a cel ,first I found the db/pk in the large loom and confirmed it was pin 2 on con 3 at the PCM , I cut it and ran both wires to the relay as per instructions , I then looked for the db/w wire my large loom only had 1 , I spliced into it , connected the ground & hooked up a switch and checked all connections. My fan came on when I activated the switch no cel , it came on at the right temp but when I tried it with the AC it would not come on and I got the cel. I looked back thru the instructions and saw the pic of the small loom and db/w wire.This is the loom that connects to con 1 on my 01 , I swapped connections to this wire and now everything works correctly and no cel. Thanks to the OP for this mod.
 
Glad it worked for you! It seems the DB/White wire in the small loom may be a better choice for those attempting this mod. Easier to find, less chance of a mix up, and I'm thinking it is actually the wire that pin A2 on Connector 1 is directly attached to.
 
(Talk about a major bump ...).

But does this work when I turn the jeep off and turn the key to on? I'd like to be able to kill the jeep, turn the key on and have the fan run for a while. Would be nice for when I shut it off offroad and it doesn't like to start back up.
 
Miller88 said:
(Talk about a major bump ...).

But does this work when I turn the jeep off and turn the key to on? I'd like to be able to kill the jeep, turn the key on and have the fan run for a while. Would be nice for when I shut it off offroad and it doesn't like to start back up.
Click to expand...

If I forget to turn the switch off when I get in and I turn the key to run my electric fan comes on. So in the way I have it wired it only runs with the key on and the switch on.

I never understood why it is a desirable thing to have the fan on after the engine is off. Specifically after the water pump is no longer moving the coolant. I mean if I had an electric water pump this would be great! I might need an extra battery... :laugh2:
 
Mudderoy said:
If I forget to turn the switch off when I get in and I turn the key to run my electric fan comes on. So in the way I have it wired it only runs with the key on and the switch on.

I never understood why it is a desirable thing to have the fan on after the engine is off. Specifically after the water pump is no longer moving the coolant. I mean if I had an electric water pump this would be great! I might need an extra battery... :laugh2:
Click to expand...

It removes some of the residual heat from the exhaust manifold, engine block,etc. My 00 will boil the fuel and run like poop on a hot restart.

So by following the method outlined prior, I can do this and have it work with just key, no jeep? Sweet!

I"m about halfway done. I got the relay wired up, just need to tap into the right wires.

After this it's extended idle
 
Miller88 said:
It removes some of the residual heat from the exhaust manifold, engine block,etc. My 00 will boil the fuel and run like poop on a hot restart.

So by following the method outlined prior, I can do this and have it work with just key, no jeep? Sweet!

I"m about halfway done. I got the relay wired up, just need to tap into the right wires.

After this it's extended idle
Click to expand...

Maybe I didn't follow the directions correctly but when I tried this mod on my 98 I got a "Check Engine" light. I had to wire mine differently. I've been using it for I guess 6 months and no issues.
 
Did this today. Very cool. The relay and wiring took about 15 min however in my 2001 xj the DB/W is not the st-run which added about an hour to the project. So I had to run a 20 amp fused line from the battery. Works great no CEL.
 
Would you happen to have a larger wiring diagram?
When I printed it, the text was too small to read.

I'm going to add the switch, thanks for your write up.
 
You must log in or register to reply here.

Similar threads

J
Question about Extended Idle
Replies
4
Views
213
Joukel
J
Four2score
XJ 4.0 cannot get auxiliary fan to run.
Replies
2
Views
158
Jeepedo129
Jeepedo129
D
Cooling Fan Switch And Temp Sensor Recommendations
Replies
10
Views
3K
DirtySouthXJ
D
M
2000 Jeep Cherokee XJ Hood Vents
Replies
10
Views
619
XJEEPER
XJEEPER
L
94 XJ Efan wont turn on
Replies
1
Views
89
Saudade
Saudade
Back
Top