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Help! Fog of Death! Dead R-DEF


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13 replies to this topic

#1 DirtyMech

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Posted 27 December 2005 - 11:34 AM

Whooo, hello everyone! Long time no type. Well I'm on the road up in California near the Oregon border, and it is cooold up here! Heavy rain predicted for days, and my 85 DL hatchback has had a dead rear defroster since the day I bought it.

Last night I checked the 20A fuse, the two connections between the resistors in the glass, and did a visual inspection of the exposed wires. Everything seems in order. Also did a multimeter test (read below for results).

Lucky me I forgot both my Chilton and Haynes at home, so you guys are my only lifeline. I only got two questions. My everlasting gratitude to anyone who gives their input!

----
1) Is there a separate switch for the rear defroster, or is it connected to the rear windshield wiper button? I know this seems like a newbie question, but its important for me because once I know I can begin tracing the circuit for a break.

I KNOW the circuit isn't on every time I turn on the key, and there doesn't appear to be a separate button anywhere on the dash. So is it connected to the R-Wiper button, yes? Perhaps its just hidden somewhere very clever.

2) I used a multimeter to test the voltage at the rear window and at the fuse. At the rear window it was about 0.25 V, and at the fuse it was a little over 3 V.

What I'd like to know is does the defroster need 12 volts like most everything else in the car? Because if it does I can just jimmyrig the thing by routing a wire from my clock lead to the positive side of the defroster circuit. Sound like a good idea? It's my option of last resort in case nobody has any words of wisdom for me.
----

Well I'm going to go back to my car and start tracing wires. I'll check back here a few times today. Peace.

#2 scrap487

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Posted 27 December 2005 - 12:17 PM

Whooo, hello everyone! Long time no type. Well I'm on the road up in California near the Oregon border, and it is cooold up here! Heavy rain predicted for days, and my 85 DL hatchback has had a dead rear defroster since the day I bought it.

Last night I checked the 20A fuse, the two connections between the resistors in the glass, and did a visual inspection of the exposed wires. Everything seems in order. Also did a multimeter test (read below for results).

Lucky me I forgot both my Chilton and Haynes at home, so you guys are my only lifeline. I only got two questions. My everlasting gratitude to anyone who gives their input!

----
1) Is there a separate switch for the rear defroster, or is it connected to the rear windshield wiper button? I know this seems like a newbie question, but its important for me because once I know I can begin tracing the circuit for a break.

I KNOW the circuit isn't on every time I turn on the key, and there doesn't appear to be a separate button anywhere on the dash. So is it connected to the R-Wiper button, yes? Perhaps its just hidden somewhere very clever.

2) I used a multimeter to test the voltage at the rear window and at the fuse. At the rear window it was about 0.25 V, and at the fuse it was a little over 3 V.

What I'd like to know is does the defroster need 12 volts like most everything else in the car? Because if it does I can just jimmyrig the thing by routing a wire from my clock lead to the positive side of the defroster circuit. Sound like a good idea? It's my option of last resort in case nobody has any words of wisdom for me.
----

Well I'm going to go back to my car and start tracing wires. I'll check back here a few times today. Peace.


ok I'm gonna look it up in my fsm... BUT I know that if everything is in working order, it should read about 6 volts on the defroster. if it reads 12 volts, your break is further down the line, if it reads close to zero volts, you can assume your break in the circuit is further up the line(closer to the battery/switch).

what car do you have? I dont know if it makes a differance but I only got a book for an ea81

#3 DirtyMech

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Posted 27 December 2005 - 12:51 PM

It's a 1985 DL 1800 EA82 2WD, 5 speed manual, with the Leone/Loyale body.

#4 NorthWet

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Posted 27 December 2005 - 01:36 PM

It's a 1985 DL 1800 EA82 2WD, 5 speed manual, with the Leone/Loyale body.

Hatchback or Stationwagon? In your first post you said hatchback (2 doors+hatch), but it sounds like stationwagon 4 doors+hatch).

The stationwagon's rear defroster has a weak point in its wiring: A connector in the rear hatch (under the main trim panel) tends to overheat and go bad; this is partly because it is under some physical tension. Of the 3 members who have posted similar problems in the last year, all three have had this same problem.

* edit - see: http://www.ultimates...ead.php?t=26724 - end edit*

#5 carfreak85

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Posted 27 December 2005 - 02:24 PM

Did DLs ever come from the factory with rear defrosters? The reason I ask is that a previous owner may have installed a rear window with a defroster grid but your car may not have been equipped to operate it. This might explain why you can't find a button for it on the dashboard.

#6 Subarian

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Posted 27 December 2005 - 02:30 PM

It should have a separate switch. On your 85, it's probably the top switch on the left side of the instrument panel. There should be 3 or 4 gray panels, and the top one should be the switch.

#7 DirtyMech

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Posted 27 December 2005 - 03:31 PM

It's a station wagon. Four doors. It's the one that came before the legacys. I don't know the chassis number...even though I should. I think its A10 or A11.

And now I've done more tests on the rear defroster, which definitely looks like it came standard. All the defroster wires are wrapped with the other wires for the car. I'd have to tear apart the body to trace all this crap by hand.

And I've also found out that the rear defroster is connected to the rear windshield wiper switch in some way. When the RW (rear wiper) button is off, I get zero volts. When it's on, I get between .10 and .25 volts. I've tested the positive lead that goes to the fuse from the battery, and it stands between 12 and 13 volts.

I had to rip a lot of stuff apart on my car, which is going to be a paint to put back. But I think a solution to this problem is at hand. Since tracing the wires is going to be nigh impossible, I believe my two best solutions are these:

----
1) Intercept the windshield wiper lead, which is also putting out 12 to 13 volts when the RW switch is on, and split it somehow so that it would send juice to the defroster. This would be ideal.

I would have to find the wire, which won't be hard. But about putting these two things in parallel, would that work? Or would there not be enough amps? I have had problems trying to do this kind of thing before....

2) My second option is to run an accessory wire (one thats only live when the key turns) straight to the defroster. This is the most attractive solution because this is something I HAVE done before for my CD player, and know it works. The only problem is that I used the clock wire directly from the clock, which means my clock is now always dead, and I don't have another lead to steal from something.

So I would need to know of a place to plug in an accessory wire that wouldn't screw something else up. Does anyone know of such a spot, perhaps under the hood that I could run a wire through to the dashboard inside the body? That would be ideal, and perhaps I could even fix my clock while I'm fixing the defroster.

So to put my Q's in short:

1) RW and RD in parallel possible? Not possible?
2) Where to plug in a new accessory wire?

#8 NorthWet

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Posted 27 December 2005 - 04:18 PM

It should have a separate switch. On your 85, it's probably the top switch on the left side of the instrument panel. There should be 3 or 4 gray panels, and the top one should be the switch.

Just like Subarian said... It should be a SEPARATE switch (pushbutton) in the bank of buttons on the left side of the instrument pod, above the headlight switch. It should be the uppermost left switch, and be denoted by a squiggly line on the button face. I can provide a picture of the switch in the car, if needed.

There is no reason that it should be related to the rear wiper switch.

#9 TomRhere

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Posted 27 December 2005 - 04:28 PM

Can't give specifics for your car, but I can offer some wiring assistance.

The rear defroster takes some serious amps to work, something in the 20 amp range I'm thinking. So you reallly don't want to tie into another circuit to run it.

Run a wire from the battery + side to a fuse, then to the normally open contacts of a relay, the other side of which would go to the defroster. Now, tap into a key "on" feed and run into a switch, then back to the coil of the relay, other side of which goes to ground or battery -.


simple diagram; x's are for spacing and don't mean anything

xxxxxxxxxxxxxxx normally open relay contacts
xxxxxxxxxxxxxxxxxxxxxxxxxx v
Battery +-----[fuse]-------l l--------defroster grid-----ground {battery -}

key "on" power feed------ switch -------(coil of relay)----ground {battery -}

#10 DirtyMech

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Posted 27 December 2005 - 08:09 PM

Ach....found it. Thanks Northwet. *smacks head* My multimeter is nearly busted. I need a new one. Don't know what the heck was causing that small spike in voltage in the defroster circuit when the wiper was on...

Now everything is back together.... The defroster is working, but not very well. Only small streaks appear in the haze on my back window. Oh well, I guess it's enough to improve visibility while driving. I think there's amps getting burnt in the wire that goes to the ground. It feels warm.

#11 NorthWet

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Posted 27 December 2005 - 08:20 PM

Check that tailgate connector, too.

#12 NorthWet

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Posted 27 December 2005 - 08:23 PM

... Don't know what the heck was causing that small spike in voltage in the defroster circuit when the wiper was on... I think there's amps getting burnt in the wire that goes to the ground. It feels warm.

Probably common ground between the wiper and defroster, and the ground connection to body is poor. This could cause a voltage drop across the connection, and apparent voltage on the defroster circuit.

#13 Subarian

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Posted 27 December 2005 - 09:49 PM

I agree with Northwet. If you're finding voltage in a circuit that's off, it's usually because there's a bad ground somewhere feeding voltage back through.

#14 DirtyMech

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Posted 28 December 2005 - 11:03 AM

I agree with Northwet. If you're finding voltage in a circuit that's off, it's usually because there's a bad ground somewhere feeding voltage back through.


Ahhh okay. Well live and learn, I guess. The one good thing about this is that I found an ACC wire on the windshield wiper button that apparently does nothing. I'm going to use it to fix my clock.

Theres SIX wires on that button, which makes little sense. Two are essential for running the windshield wiper, and a third powers the motor when the switch is turned off so that it returns to its proper resting position. The other three....no idea. One is nearly no voltage, possibly a ground, another is around four volts, and the third is 12/13. Disconnecting the 12/13 volt wire, the yellow one, I found no change in wiper function. So to the clock it goes!




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