Manning

OK, so my rear hatch glass defrost doesn't seem to want to defrost (demist?). I have carefully gone over the entire thing with a magnifying glass looking for breaks in the little lines but there aren't any. BUT, here is what I have found:

If I use a volt meter and ground one end and touch the other to the connector on the end of power feed wire that connects to the lowerend of the drivers side hatch strut I get like 11 or 12 volts. If I then move up to the lead coming off the top of the strut I get no voltage reading at all. Hmm, seems odd.

So I touch the probe to the tab that the power feed wire plugs onto and I still get no reading. How can that be? I just tested the wire on its own and I get power, but plugged onto the tab I get nothing. What gives? Where is that electricity going. How does this stupid thing work? Do I need to replace the hatch strut?

I hate electricity sometimes.

Manning

Bump

No seriously folks, there has to be someone out there amongst you superstars who knows something about the rear window defrost. This has been bugging me for over a year...

HELP....

Dan Wray, how about you, can you help?

SoCal Driver

The strut on the drivers side is just an insulated conductor for the current that goes to the defroster grid.

The strut on the passengers side is also a conductor BUT the end that attaches to the car has a contact inside the socket to ground it through the ball on the pillar. This strut also has a protected contact at the pillar end for the rear cargo area light.

So use the continuity part of the ohm volt meter and see if the pass side hatch strut grounds out to the body from the soldered on connector for the grid on that side.

Use the volt meter to check for current coming to the heating grid on the drivers side grid connector to ground.

gleamingred944

SoCal is right - 90% of the time the problem
is one of the 2 connections to the strut or the sliding contact in the strut. They can be intermitent too - like touching them can change things! Clean them all off and make sure they have spring to them. Both sides, remember - the return current comes back down the other side strut from the power feed on at least some models (e.g. mine).

Manning

Well dang. I think I described my first problem as getting no voltage up the drivers side strut. I think I'll pull that off and see about hosing out the lover cup with contact cleaner. Maybe theres dirt and lube buildup in there and cleaning it will return continuity. I haven't checked for continuity so much on the passenger side yet since I wasn't getting power up the drivers side.

Thanks for the help so far.

SidViscous

Check your fuse too. Had a similar problem. Problem is when working it seems to really heat up the fuse, after awhile mine looks all burnt up and ****e. After awhile not enough current can get through to heat it up.

I keep a bunch around. each fuse only lasts like a week for me.

Probabaly need to rienforce those grounds in the back.

Manning

Yeah, I checked the fuse and have replaced the relay. I get power to the wire, but when I actually plug the wire onto the tab on the strut and check for voltage I get nothing.

Robby

I'm not good w/electrical probs & this may be a stupid question, but, do you have electric mirrors? If so, do they defrost like they are supposed to? Not sure if this would tell you anything, but, if they DO work fine, then it might help narrow this down a little...

SoCal Driver

Manning,

The drivers side strut does not ground out.

The passengers (right) side does.

So there is no reason to clean the cups on the drivers side strut.

The only cup that has this contact is supposed to be the one on the passengers side (right) and only on the pilllar.

Manning

Well, here's the deal. I used to have electric mirrors and they worked fine (defrost-wise) even though the rear defrost stopped working. I have since removed the electric mirrors, since I think they are kind of silly, and replaced them with manual mirrors. I thought perhaps I would have to jumper a connector someplace to make sure the rear defrost still got power. Apparently this is not the case since the lead still energizes when I cut on the switch on the dash.

Manning

SoCal,

I'll take pictures tomorrow night (have to use camera at work) and show you all what I'm looking at. That might help some.

Basically there is a lead that comes out of the trim on the drives side (DS) and connects to a blade type connector on the bottom of the DS strut. Then a lead jumpers between the top of the strut and the blade on the window glass. One the passenger side (PS) there is a similar setup, except the PS strut has a cup thing at the bottom and the wire that connects to it and goes into the trim is smaller and doesn't energize at all.

SoCal Driver

The small wire on the PS coming out of the pillar is for the cargo light. There is a contactor under the plastic cup just for this. As the hatch is opened the contact hits the steel of the rod and the rod is grounded through the socket at the PS pillar.

The large wire coming out of the DS pillar is the power wire for the heating grid.

I would test this using a volt meter or a test light with one side grounded to the chassis and checking for power at the DS pillar wire, then the jumper from the DS strut to the heating grid. Move to the PS and check the grid connector then the connection at the strut. Last the actual shaft of the strut.

Manning

Well, off to the garage with the volt meter...

IceShark

Michael, the other item you want to look into is a break in the wires inside the insulation from flexing or snagging them with cargo. Try the old squish and wiggle the wire routine. I had one of mine go out in this fashion.

Manning

OK, so I pulled the DS strut off and tested it for continuity and it was fine. That was odd, since it didn't seem fine on the car before. So I put it back, still fine. Good now we're getting somewhere.

So I test to see if I'm getting voltage to the top of the strut. Yes, now I am. Good.

Test to see if I am getting voltage to the grid. Nope. So I pull off the wire and test for continuity. Yes, about 1 ohm.

I test across the grid. Yes, continuity. Good.

Test the other jumper wire. 8 ohm. Hmm, alot higher.

So, I make up a pair of jumper wires and test them. 1 ohm. Well, that's the same as the first wire, so I put it back in place after I clean off everything with contact cleaner. Low and behold I get continuity all the way from the lower contact to the other side of the grid. Woohoo! I still need to check voltage across the grid, but I think I am close to sorted.

I think I am back in action. Thanks for the help!