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Late Model Rear Defrost Switch Wiring???

Kirby N.

NAXJA Forum User
I have been trying to figure out how the wiring works for a late model rear defrost and I have way more time in it than should be neccessary. Here is basically my dilema:

I have a Bestop Hard Top on my TJ with defrost. My Tj came with a soft top from the factory and therefore doesn't have the stock switch for a rear defrost.

I got the defrost switch from a 1999 Jeep Cherokee for my TJ. From experimenting with my Dads Xj I figured out that the four wires are for:

Power when Lights are on for illuminating the switch
Ground
Relay (ground)
Power when defrost is on

I wired it all up and it worked, except the timer doesn't. It comes on when I hold the button down only. I thought maybe there is a time somewhere, so I went to Jeep and looked at a harness made by Jeep to add a factory hardtop to a jeep. No timer to be found. I thoguht for sure the timer must be in the switch, now I haven't a clue. I even checked to see if XJ and TJ switches are the same. They are.

Any help would be appreciated. I got a fog light switch and took the cover off and tried to make it work too, but now I can't make that switch work either.

Thanks!

Kirby
 
There is a timer, but it's built into the instrument cluster. Does the defogger switch at least stay lit after it's pushed once, or does the light only work when held down?
BTW, Jeep fog-light switches are junk. I went through two at $24 each before giving up and wiring a new switch myself.
 
I think you may have blown the switch. It looks like you may have grounded one that should have been +. With the pinouts facing you, and with the gray tab up, the pins are (left to right):
1. ground
2. defogger switch sense [here I assume the FSM to mean sensor]
3. fused defogger relay output
4. dimmer switch
 
I don't know about the latest ones, but the earlier ones have a timer built into the relay. The switch is a momentary-contact switch, not meant to stay on. The relay is flip flop relay, which changes state each time the switch is pushed, and also has a timer to shut it off after about 10 minutes.

I happen to know this, because I was trying last year to figure out a way to use a garage-door remote opener to operate an outside light on my garage, and needed a simple flipflop relay, and I just happened to have some XJ bits around and... etc. etc.

On the 95 and XJ's of that era, this relay lives in a relay cluster that is underneath the dashboard, near the center. It's red, and has a little tag identifying it as a special relay.
 
It is not in the relay because I went and got a factory relay and I am using the factory wiring from the loom out to the fuse box on the fender. The wiring comes in the firewall and terminates at the large loom plug under the dash. This is where the wiring goes into a blank socket, making sense that it would go into the instrument cluster and into a timer, then back out to the switch.

Timber: The switch is not blown. After I got it all wired and it didn't work, I took it out and swapped it into my Dads Xj and it worked fine in his wiring.

I am not sure off the top of my head what I wired the specific wires to, but my guess is that the #2 one goes into the instrument cluster to a timer then out to the relay. I wish I knew where it went into the cluster and if I could splice in to it somehow.
 
Kirby N. said:
It is not in the relay because I went and got a factory relay and I am using the factory wiring from the loom out to the fuse box on the fender. The wiring comes in the firewall and terminates at the large loom plug under the dash. This is where the wiring goes into a blank socket, making sense that it would go into the instrument cluster and into a timer, then back out to the switch.

Timber: The switch is not blown. After I got it all wired and it didn't work, I took it out and swapped it into my Dads Xj and it worked fine in his wiring.

I am not sure off the top of my head what I wired the specific wires to, but my guess is that the #2 one goes into the instrument cluster to a timer then out to the relay. I wish I knew where it went into the cluster and if I could splice in to it somehow.

Are you sure they gave you the right relay? I'd be a little surprised if they changed the design and put the timer outside the relay. On the ones of my era the relay is self-contained. If the switch is like the one in mine - push to start, push to stop, then the relay must be a flip-flop, which changes its state with each switch impulse, not the regular type, but either type will fit the socket. Your symptom of having to hold the switch down suggests to me that the relay is the wrong one (or defective). If you have another XJ with a similar setup, how about swapping out that relay to test it?
 
Langer, I'm not sure what you're looking at for an '00, but from the 2000 FSM (bad pic, but I'm at work and this is the best editing I can do here):
defogger2.jpg
I'll help you out--both the timer and the "switch sense" are in the instrument cluster. The relay is in the junction block.
 
Thank you Timber. I can't see much from that picture. I really appreciate you looking into it.

Matthew- It isn't the relay. I tried a relay from my buddies 2001 and it is the same # and doesn't change a thing. So it the right relay and it is not blown. The relay is in the kick panel on the passenger side and on the passenger fende on my TJ.

The more I think about it the more it makes sense that the timer is in the instrument cluster. When I wired it I was able to use some of the factory wiring. The factory wiring actually comes up from the relay and terminates under the hood where the wires come into the wiring harness plugs. It just stops at the plug with blanks where it comes into a big plug. So I tapped in there and ran a couple of wires right to the switch. One for the Relay that goes out to switch the relay and one for the indicator light that signals it is on. Then the one for the indicator for the switch was actually the power post-relay for the defroster. If the timer was in the switch, the second wire would be unneccesary because the switch would have the light wired in. Since the witch just trips the timer and the timer turns it on, it makes since that it would need a seperate wire for the indicator run directly from the power wire for the defroster.


Did that make no sense?

I have discovered that defroster switch can be altered to act like a fog light switch easily. I would like to have the timer still. There must just be an in and an out right? I wonder if I could just look through it and figure out what wires aren't being used.

Thanks again!

Kirby
 
From the junction block to the instr. panel, the wire color is light blue/white, and then from the instr. panel to pin 2 of the switch the color is dark blue/white.
 
Ok I will look into it when I get the chance. I know I spliced into the light Blue/ White from the cluster and I just ran it straight to the switch. Hopefully the cluster will have a wire or something there that I can figure out where it goes in. Thank you!
 
Hi there, I have a 01xj and the rear defroster works only when I keep the switch engaged. I've looked everywhere and can't find info on the timer. I see here that it's in the gauge cluster...but how do I test it? Is it possible to fix, or does the whole cluster need to be changed? Thanks for any info😊

Sent from my LG-H873 using Tapatalk
 
Hi guys. I have the same problem. Is there any way to fix the timer in the cluster? Did you find out? The car is in Norway, so its very hard to find a new cluster with metric km/t here. Tired of icy wondows and mirrors :)
 
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