[USMC_XJ]

Note: This is intended to be a cheap, alternate solution to turning your auxiliary fan on/off. I used some wire and a toggle switch. If this does not work for some of the 97+ XJ's and throws a CEL, I am sorry. It is a hit and miss with those. If you can not do it this way, don't waste time trying to use a relay and utilize the PCM, just run a relay to power the fan. Using even more relay is pointless.


I have searched this forum and did not find anything like this, so I figured I would post it. I did this mod on a 94, but will work on 88-01. (See update at bottom).

Most people have just added a switch with a relay, and then directly to the fan. I (being broke at the the time, and nothing to do) decided to have a go at this and try to find an easier way to do it.

The fan gets power through a relay in the PDC under the hood. From the relay are four wires, they are Green, Green w/ red stripe, Blue w/ white strip, and Dark Blue w/ pink stripe.

It took me like 30 minutes to try to figure out what went to what, and in the process of figuring out the wires, (before I pulled the PDC out) I accidentally supplied 12V to the ignition ground, asd, and the I.O.D. fuse.

I then had to figure out what one went to where. According to Haynes, the green w/ red stripe was direct 12v, the green went to the fan, and the blue w/ white stripe went to a ignition activated 12v source. The dark blue w/ pink stripe went to the PCM.

I couldn't figure out how it worked, then it dawned on me. When the PCM sees that its getting hot, or the a/c is selected, it connects the dark blue w/ pink stripe to the ground activating the fan. There is no power going to or from the PCM through this wire. All it does is connect the ground side of the relay to the PCM. Internally, the PCM handles the rest.

Once i figured that out, it was pretty simple what to do, just splice a wire into the dark blue w/ pink stripe wire going into the pcm. (It is pin 31 on 91-95 and for 97-01, it is pin c2 on connector C3.) Then run that wire into a toggle switch and connect the other side to the ground.

This shows the DB/PK wire that you need to find and splice into:


This is the splice. I chose to use a male and female connector. There is no current flow through it, so it will be fine. (It's the male/female connector on the middle left)


And here is the switch:


**Update**
Thanks to Kettles, this is the wire that you need to splice into on the 97-01's.

Also, thanks to TheSandman, this is also the wire that you need on the 96 XJ's.


**UPDATE** - After looking at 3 different FSM's, they showed that it always uses a dark blue w/ pink stripe. After some reading, it shows that for 96-01, the wire is indeed a dark blue w/ pink stripe. It goes into the pcm at connector C3 and is pin c2 for 96-01. (Make sure that it is a dark blue wire w/ pink stripe). This will work for 91-01 Cherokees.

*Just a note. Kettles and Carves (both 97+) have NOT received a CEL by doing this. HOWEVER, it seems to be a hit and miss.

For 88-91, it shows that it is not controlled by the computer, but just by the radiator pressure switch and/or a/c. It is always grounded, so you would have to put 12V to the orange/black or gray/ black wire going into the Fan Cooling Relay. Again, this is only for 88-91 Cherokees.

There it is, you're done.

You can now turn on the fan any time the ignition is on, and it will still work if the switch is off because the computer can still control it.

[USMC_XJ]

Bump for anyone who has successfully done this on a 96.

[xjarchaeologist]

Very nice. I've been wanting to do this without setting off the CEL for a while...

[Holder350]

Did it today on my 95.....but its still the same OBD1 system like yours.

[USMC_XJ]

Originally Posted by Holder350

Did it today on my 95.....but its still the same OBD1 system like yours.

I know that the PCM is the same is from 92-95, and the PCM is the same from 97-01. 96 is a weird year as the PCM is different from the 92-95 and 97-01. I know the wire is still dark blue w/ pink stripe, put don't know what pin # it is. Glad it worked for you though.

[ehall]

Good info except the years--the Chyrsler HO engine managment was introduced in 91 not 92

[USMC_XJ]

I knew the PCM was the same for 92-95. I didn't know any further back. I'll add that.

Thank you.

[stoneytj]

well i know what i'll be doing this weekend.

great write up seems super simple, almost to simple.

i'll be doing it on a 00 if that helps ya out at all

[Kettles]

Buckeye, I have a good photo of the wire that needs to be spliced (and of it spliced) at the Connector if you want to use the pic. I am a visual learner and your picture doesn't really help me, so I thought maybe some others would be in the same boat.

This is from an 01..

[USMC_XJ]

Originally Posted by Kettles

Buckeye, I have a good photo of the wire that needs to be spliced (and of it spliced) at the Connector if you want to use the pic. I am a visual learner and your picture doesn't really help me, so I thought maybe some others would be in the same boat.

This is from an 01..

Thanks Kettles. I'll add it to the post.

(I only have a camera phone)

[Kettles]

Originally Posted by BuckeyeXJ

Thanks Kettles. I'll add it to the post.

(I only have a camera phone)

Dont we all.. Thats an iphone photo, lol. Its all about holding you hand still, and having enough light. Do that and phones take good pics. I dont have money for a real camera, i have a jeep! And I want another!

[USMC_XJ]

Originally Posted by Kettles

Dont we all.. Thats an iphone photo, lol. Its all about holding you hand still, and having enough light. Do that and phones take good pics. I dont have money for a real camera, i have a jeep! And I want another!

I was trying. LOL. I guess I'm just not as talented as you.

My girlfriend has a Nikon D80, but she won't let me use it.

[Carves]

Originally Posted by Kettles

Buckeye, I have a good photo of the wire that needs to be spliced (and of it spliced) at the Connector if you want to use the pic. I am a visual learner and your picture doesn't really help me, so I thought maybe some others would be in the same boat.

I have a BETTER piccy ..... ...

But no photo posting priveledges ....

So my contribution is a warning ...

Ensure that it is the Blue/Pink wire before splicing at the connector ... as there is a Blue/Red wire right next to it ... as can be seen in Kettles post photo.

Since we have the steering wheel on the correct side of the vehicle over here ... ............... I tapped in at the fuse box, drilled a hole/fitted grommet in the firewall and went straight to a switch on the dash .... and just coz I am a bit OCD about this stuff ... I even used a spare Blue/Pink wire from another harness ...

Still no CEL happening ... so I'm happy.

[USMC_XJ]

Originally Posted by Carves

I have a BETTER piccy ..... ...

But no photo posting priveledges ....

So my contribution is a warning ...

Ensure that it is the Blue/Pink wire before splicing at the connector ... as there is a Blue/Red wire right next to it ... as can be seen in Kettles post photo.

Since we have the steering wheel on the correct side of the vehicle over here ... ............... I tapped in at the fuse box, drilled a hole/fitted grommet in the firewall and went straight to a switch on the dash .... and just coz I am a bit OCD about this stuff ... I even used a spare Blue/Pink wire from another harness ...

Still no CEL happening ... so I'm happy.

Why can't you post pictures?

Thank you for the caution. As stated, I blew a couple fuses trying to figure out how to wire this.

There is also a dark blue w/ orange wire in the PCM. So be very careful.

[Carves]

Originally Posted by BuckeyeXJ

Why can't you post pictures?

Jeep Forum doesnt host pics on site ????

I dont use photobucket etc ....

But if you grab your passport and click on this link I just tidied up ...... ..

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