Rear window defogger is stumping me.

If I'm reading this right, if you're getting 12V on both sides, the ground circuit is open.

Except for this:

There's no way that could be happening if one side was open or if the trace being measured was open.

No, I meant that if I put a probe on each side of the grid, I read appx. 12 V across them. However you were right anyway; on a hunch I pulled the trim and pulled the wiring out where it goes through the bellows seal at the to p of the liftgate; ground completely broken. So apparently that grounds to the hatch somewhere and I had enough of a ground to show voltage but not e nough to make it work right. Also one of the wires for my CHMSL is hanging on by a strand and three more wires show signs of chafing, so I guess I kn ow what I'm doing this evening...

What you're saying is true, but his measurements are contradictory. how can the voltage drop as he moves across the grid, and them jump back up to 12V at the end? At least, that seems to be what he said.

What would have made the CHMSL wires fatigue? Do they move every time the lift gate is open.

Ah.

Which is why you need to be very careful when using a high impedance voltmeter. Sometimes it's best to do this sort of thing with a instrument lamp bulb with a couple of pieces of wire soldered on.

Yup, same bundle. CMHSL is in the liftgate not the body of the vehicle. T he harness that I pulled out has the rear defog, tag light, rear wipe/wash, CHMSL, and something else unused (power locks?) all in the same harness, a nd it goes through a hole in the body with a sharp edge and only electrical tape for protection (yes, the harness is apparently wrapped with adhesive tape.) Thanks, Chrysler! I think I will buy a stick of door edge molding to cover that sharp edge so it doesn't happen again in another 15 years.

Seems to be working now, I can't test the CHMSL until it gets dark and I ca n't give a 100% thumbs up on the defog, but since the trim is now off I was able to pull the connectors off the window and I was reading 17 amps so I assume that's good.

nate

. 12V across them. However you were right anyway; on a hunch I pulled the trim and pulled the wiring out where it goes through the bellows seal at th e top of the liftgate; ground completely broken. So apparently that ground s to the hatch somewhere and I had enough of a ground to show voltage but n ot enough to make it work right. Also one of the wires for my CHMSL is han ging on by a strand and three more wires show signs of chafing, so I guess I know what I'm doing this evening...

yeah, one of these days I am going to buy a nice test light with an incande scent bulb... probably ought to have one already, but I don't.

The value of all my tools, if I had to replace them with new, is likely mor e than my car, or even a modest house in a less affluent neighborhood. And yet there are so many tools that I still don't have.

Bad ground. You have voltage but not enough current to make the grid work. Run a jumper to a good ground to verify.

Welcome to the club.... I'm not sure it's a good thing to be on a first name basis with 3 different tool truck operators...

Maybe it had a grommet that long ago disintegrated.

Seems like there was a TSB on that harness. Something to the effect of new wire/wrap with harness tape and a clip to hold it in place.

I wouldn't drive any Cherokee anywhere. Those Quadra-Drive ones make me nauseous just pulling around the shop parking lot.

GW

"Steve W." wrote in news:ldm9m4$cb6$ snipped-for-privacy@dont-email.me:

I second that.

Bad grounds can create the very weirdest effects. I once had a problem with my Integra's brake lights that I traced back to a bad ground. My reading of the EWDs told me that the problem I had was not possible, but it did happen.

XJ 'box' Cherokee, not Grand. Other than just general noise, it's rather p leasant to drive, at least given that it's an el strippo 4WD vehicle. Driv es pretty well - exceptionally well when you remember it's got a straight f ront axle and has a rather high COG compared to a regular car.

But my understanding is that the grand is very similar mechanically other t han transmission, xfer case and rear suspension...?