rear defroster

pass1over

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Rear defroster stopped working awhile back and I discovered one of the tabs had come detached from the grid. I bought a kit, followed instructions and put it back on the grid. Rear defroster worked for about two weeks and now it doesn't again.

Both tabs are attached firmly, and I get power at connections with a multimeter. There are no breaks that I can see in the grid.

When re-attaching the tab, do you put it back in the same spot it came off from or attach in a new location? I did new location, figured better connection.

What else should I check? I'm assuming it's an issue with that tab I re-attached?
 

travelers

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I re-attached mine in the same place on my 85 vette and had no problems. The grid has a specific ohm resistance which you may have changed with your new location.
 

pass1over

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I guess I'll try to detach and reattach in original spot. The instructions with the kit said to pick a new spot on the grid, but other instructions I read online elsewhere said to reuse same spot.
 

redfirepearlgt

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Rear defroster stopped working awhile back and I discovered one of the tabs had come detached from the grid. I bought a kit, followed instructions and put it back on the grid. Rear defroster worked for about two weeks and now it doesn't again.

Both tabs are attached firmly, and I get power at connections with a multimeter. There are no breaks that I can see in the grid.

When re-attaching the tab, do you put it back in the same spot it came off from or attach in a new location? I did new location, figured better connection.

What else should I check? I'm assuming it's an issue with that tab I re-attached?

Assuming you are getting 12-14 vdc from the Rear defroster relay via F52

The rear defroster mesh is the load for which the voltage drops across. Therefore there should be no voltage present on the ground end with respect to ground. If you are reading 12-14 vdc on both Brown/Light Blue wire and the Black wire on the other end of the defroster grid, that indicates you have an open to ground on circuit. Shut the defroster off. Check disconnect the source (Brown/Light Blue wire) on the defroster grid. Then go the other side of the window defroster and check that wire (Black) connection to ground. It should read less than 1 ohm. If it does not there is your problem. If it checks good, read the resistance across the defroster grid. on the connectors. It will read some form of resistance. My calcuation using ohms law and assuming the circuit only draws 15 amps of current, the defroster grid should be about 0.8 - 1.1 ohms. (E/I=R). Anything higher slightly higher will only result in a slower defrost or a possible failure on the connection point in the future where the high resistance is being created.

I repaired a Saturn Aura Rear defroster by simply soldering the wire directly to the grid after the tab gave out and came loose. Worked fine that way for years. Sleezy fix, but resolved the issue without having to replace the rear glass.

Color codes are IAW Ford 2005 tech manual on line.

Good luck
 
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pass1over

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I do get 14 vdc when I probe the terminals. I will probe them in relation to ground and check for an open ground on circuit.

Thanks for the info!
 

pass1over

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Kind of a pain to have to have the car running while checking the voltage on this. Any way around it?
 

pass1over

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Key on/engine off can still provide power to the defroster, if that's what you're asking.

doesn't in my car. key on, engine off, I get no power to defroster. It's not until engine is running that the circuit is powered.
 

redfirepearlgt

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Kind of a pain to have to have the car running while checking the voltage on this. Any way around it?

You don't need the circuit energized to check for an open to ground. Use continuity. Disconnect the black wire from the defroster grid. Connect your red probe to the black wire. Find a clean chassis ground anywhere nearby. Connect the black probe there. With the meter set to ohms you should read less than 1 ohm resistance. If the meter reads infinity or a high resistance value, you have an open to ground on that wire. All of your voltage checks up to this point to the fact that ground is not present....thus open to ground.
 

pass1over

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disconnected both plugs from the grid. Probed drivers side and ground and was getting a number (it kept fluctuating), passenger side probed to ground got nothing, probed across the grid and got the .8 to 1.1 'ish like you calculated.

Seems like the passenger side is still the problem, does that mean it's in the wire itself? Or do I need to reapply or attach a new terminal to the grid on that side?

BTW, passenger side is black w/grey stripe and drivers side is solid black.
 

travelers

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According to the WD, the black/grey stripe is power and the black is ground. So try checking the black wire to ground for continuity. There is 2 fuses F6 and F39 along with a rear window defroster relay which is controlled by the HVAC Module.
 

pass1over

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have continuity when I probe black wire to ground
fuse 6 and 39 under the hood are both good
swapped wiper and defroster relays, wipers still work, so I assume they're both good


Like I said earlier, the tab I reattached I put on a new spot on the rear glass grid spot, not the spot it popped off from. Should I detach it and reattach in the original spot?
 

redfirepearlgt

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If you still read the same resistance on this tab across the heater grid (for no better term) then you should be good. However if you aren't try to re-attach to the original point if possible. Without being there and seeing everything it has to be something stupid we are missing. The ground is there, the load is there and the voltage is there with the rear defrost switch turned on. Sorry man I can't help you further at this point. Wish I was local I would be glad to give you a hand...and with winter coming on it would be nice to be in a warmer climate. Let me know if you need me to look at anything else or you have any other questions.
 
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pass1over

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indicator light comes on, I get like 14-15V at the black/grey wire with car running. I"ll check again to make sure though.

I agree, gotta be something dumb, I do appreciate all the help so far.

It worked for awhile after I reattached the tab, then just stopped one morning. Wondering if it's like corrosion where I reattached the tab or something. I've never removed them before, just use a solder iron?
 

redfirepearlgt

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I fixed the rear defrost on a 2007 Saturn Aura by soldering the power wire straight to a point on the copper exposed area. The tab that hte wire attached to had built up high resistance and caused the solder joint to get hot enough to fatigue which finally casued the solder to give way. Reconnecting the tab proved fruitless with the equipment I had, so I cut the female connector off of the power feed wire, tinned it and the exposed area on the heater element in the rear window and soldered the wire directly in place. Worked like a charm and never had any further issues with it.

So yes you could do what I did if there is enough exposed area.

One other thing to check however before you go to this level if I could add.

Connect the power feed wire to the element. Disconnect the ground side. THen backprobe the power wire through the insulation with one probe and touch the other to the ground connection side of the element. If you read anything above the resistance you read when directly checking the element (grid) for resistance you have a connection issue with the connectors themselves. A pushed connector on the wire side, a spread spade connection the gets loose and builds up resistance, something along that line. You may need a sharp item to poke through the insulation. When I have to do this at work I use a hat pin, and then connect the probe to the hat pin via an alligator clip lead. Check both sides of the element in this manner.

The very last thing I can think of while sitting here waiting for a work order to come in, is to check your wiring from the switch on the defroster panel back to the element. THere may be an open that has developed there from a possible pinched wire or even a possible fusable link that the prints fail to show. You should read continuity from front to back when checking the back/gray wire. You will also need some extra wire to make the reach....OR simply ground the wire to the chassis on the element end and then pull the wire off on the power button and check that wire to chassis ground. If you do it this way check it isolated from ground first (should read open or infinity) then connect as I explained at hte defrost element and then probe the black/gray wire at the button to ground. Do this obviously with no power on the car....don't even put the key in the ignition just to be safe.

That's the last trick in my hat I can throw at it to help you. Best of luck. Hope this makes sense. If I wasn't clear enough let me know and I will try to better explain.
 

pass1over

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I've had to reattach this tab a few times now. Had decent luck with soldering it straight to the back glass. The last fix lasted probably 2 years. But it popped off again a few weeks ago and I'm having a hard time getting it to stay.

I was thinking, since JB weld is metal impregnated epoxy, would that possibly work? Is there enough metal in there for it to complete the electrical connection and my defroster still work?
 

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