Rear Window Defogger & Gauge Cluster

I've searched high and low for an answer to this problem within the forums, to no avail...here's the deal.

I have a '00 XJ with an inoperative rear window defogger. I've followed the troubleshooting steps in the factory service manual. The switch is good, the relay is good, the defogger grid on the window is good. That leaves me with only one option, I think, and that would be the timer built into the gauge cluster.

1. Is the only solution to this problem replacing the cluster?
2. Instead of replacing the cluster, can I bypass the timer by shorting the dark blue w/ white stripe and light blue w/ white stripe wires that go to/come from the timer?
3. Can I buy a timer to insert into the circuit in place of the cluster's timer?
4. Can I simply replace the relay with a similar one that has a timer built-in (which I believe is used in pre-'96 XJ's?)?
5. Any other ideas?

Any insights appreciated. Thanks much!

Have you checked the wiring between the grid and relay? I fixed a neighbors wiring by the back hatch. Does it light up the switch indicator when it is on?

Hey Jeepm@n,

Thanks for the reply. Yes, the switch light functions correctly. And, there is power to the grid, and the grid is unbroken.

I believe the ground is OK, but perhaps the timer isn't permitting closure of the circuit?

macidgit said:

Hey Jeepm@n,

Thanks for the reply. Yes, the switch light functions correctly. And, there is power to the grid, and the grid is unbroken.

I believe the ground is OK, but perhaps the timer isn't permitting closure of the circuit?

Click to expand...

If you have power to the window's grid, and there is a ground, either the grid is bad (you said it tested good), or you have missed something.

On reflection, you must be right...guess I'll doublecheck the ground. Thx. I'll post the fix, if I find one! :roflmao:

You said the switch light functions. If that means it lights up when you activate it and then shuts off a while later, that indicates that the timer IS working. Right?

Actually, I've never let it run the full 10 minutes, though that is a test I can try. However...

I rechecked the ground continuity from the ground side of the grid to the body, and it seems good to me... 0.001 ohms. BUT, is that too much resistance? Does that indicated a loose ground possibly?

I just checked the supplied voltage on both sides of the grid with the switch on and off with the engine running. Results:

Switch ON, grounded to chassis through multimeter
+Side V = 13.9

Switch ON, measured across the grid
+Side V = 12.2
-Side V = 11.7

Obviously with only 0.5v drop across the grid, there isn't going to be much current flow and hence no heat to speak of.

Since all the grid lines seem to have continuity individually across the full width of the grid, is this an indication that one of the connection tabs is not truly connected?

Since you have power at the positive end of the grid, and slightly less at the negative end, I'm going to point the finger at the ground side wiring.

Yes, I'll run the ground side wiring to ground (LOL) tomorrow and post whether or not that solves the problem. Hopefully so!

Recently I read about a better way to check grounds than resistance. Check voltage with red on ground side of grid and black on a true ground. If ground circuit is perfect, you should get 0 volts. IIRC, more than one volt was excessive.

Recently I read about a better way to check grounds than resistance. Check voltage with red on ground side of grid and black on a true ground. If ground circuit is perfect, you should get 0 volts. IIRC, more than one volt was excessive.

Click to expand...

Yes. I just went through the FSM test procedure, and they instruct to do just as you said, with the defogger switch on. I did, and it failed that test. I'll get the numbers and plug back in here tomorrow morning. Thanks for the tip!

At the lowest resistance setting of the meter, you'll usually get a little resistance because it's reading its own fuse. Don't worry about small fractional ohms.

macidgit said:

I've searched high and low for an answer to this problem within the forums, to no avail...here's the deal.


I have a '00 XJ with an inoperative rear window defogger. I've followed the troubleshooting steps in the factory service manual.

Click to expand...

Is the troubleshooting steps available anywhere online. Mine is a '00 also. I just found out my rear dofogger is not working. The side mirror heaters ARE working though. I was kinda thinking maybe it was a wiring issue but if I can troubleshoot things to narrow it down that would be great.

Thanks

Re: Rear Window Defogger & Gauge Cluster

How long is the timer supposed to for before it shuts off. i never paid attention when it was working right since it was working right?