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#1873138 - 10/01/09 11:27 AM Rear Defrost doesnt work?
Kinger87 Offline
Poobah

Registered: 12/15/02
Posts: 7606
Loc: Gladstone MI
on a 98 crown vic. I searched around and didnt find anything. Obviously the fuse's.. relay and such are in good shape. anything else stupid obvious to look for?
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"Responding to a question by saying do a search, look in a auto parts catalog, or call a mechanic isn't being helpful"

2001 Crown Vic, Hpp package, air bags n all. stock as can be.


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#1873141 - 10/01/09 11:31 AM Re: Rear Defrost doesnt work? [Re: Kinger87]
Colt45 Offline
less is more©
Poobah

Registered: 08/30/04
Posts: 6352
Loc: Moses Lake, Wa
Check the window circuit itself.
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2004 Ford Crown Vic LX, 72k "Tank"
2002 Ford Crown Vic PI, 159k "Highwayman" (Ex-Kootenai County, ID Unit #42)

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#1873242 - 10/01/09 01:03 PM Re: Rear Defrost doesnt work? [Re: Colt45]
metro21 Offline
Climber

Registered: 03/13/09
Posts: 578
Loc: Sacramento, CA
My experience: I had the old cheap bubbly window tint taken off my rear window and replaced with a new professionally installed one. After that the defroster lines stopped working. I checked everything and poked around with a tester but could not figure it out why until one day I was looking out the rear window with the sun coming through and saw that when the tint was taken off so were much of the defroster line material off the top of the lines. The lines were still there but I could tell the difference in darkness in the lines and where pieces in the line were not as dark as others.

One would not have been to tell this from simply glancing at the window without a bright source of light coming through as the lines appear perfectly normal still from inside and out. My only option then was to replace the window and then have it retinted and that just wasn't worth it to me. I don't use it THAT much here in CA.

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#1873318 - 10/01/09 02:57 PM Re: Rear Defrost doesnt work? [Re: metro21]
Kinger87 Offline
Poobah

Registered: 12/15/02
Posts: 7606
Loc: Gladstone MI
the little light on the button wont come on at all. does this mean a problem with the window circuit itself or something else? and how do you go about checking the window circuit, other than just shining a light through the little lines?
_________________________
"Responding to a question by saying do a search, look in a auto parts catalog, or call a mechanic isn't being helpful"

2001 Crown Vic, Hpp package, air bags n all. stock as can be.


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#1873595 - 10/01/09 11:07 PM Re: Rear Defrost doesnt work? [Re: Kinger87]
Tracy Offline
Over the Hill

Registered: 09/07/09
Posts: 3822
Loc: Kewaskum, WI, USA
If the light won't come on then it's either the fuse or the switch.
Most likely the fuse.
_________________________
1999 Deep Wedgewood Blue & Rust P71, 20x,xxx miles, full cloth interior, 3L55 RAR, BH1976 Headlight Relay Harness, and a few other mods. Former Chippewa Falls, WI PD car. I'm the 3rd owner of car.
Now with Mustang Wheels, Honeycomb Grille, and Ford AM/FM CD player with RDS.



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#1875549 - 10/04/09 09:52 PM Re: Rear Defrost doesnt work? [Re: Tracy]
Lad28der Offline
Member

Registered: 03/13/09
Posts: 151
Loc: Bellmawr, NJ
I have the same exact problem on my 95. I've even changed out the whole switch and it doesn't work exactly like the original. I don't know if this has anything to do with it buy my interior dome lights and trunk lights don't work either. Any more ideas?
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2004 P71 Ex-NY State Police, 90K--BBK 70mm TB, aFe Cold Air Intake, SW Long Tubes, Custom 2.5" X-Pipe w/ Magnaflow Cats, Flowmaster Super 10s and 3" Tips, Bumper Tuck, Havis console, Sony Head Unit, 8K HID's, 5% tint all around, Setina PushBar...More to come

(Work In Progress)1995 P71 137K from Lansdale PA police dept
-Police Package,Flowmaster 40 Deltas, Moog Front Sways, Custom intake w/ K&N filter.

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#1875568 - 10/04/09 10:06 PM Re: Rear Defrost doesnt work? [Re: Lad28der]
LTDteether Offline
Over the Hill

Registered: 07/19/02
Posts: 4446
Loc: Democratic Rep. of Southpaw
The switch grounds a pin on the LCM. If the ignition is on, the LCM grounds the defrost relay in the battery junction box. The relay then provides power to the defrost grid and to the indicator light. You indicator light is not going on so the relay is not pulling in.

Does the switch illuminate when the instrument illumination is active? If not, the ground may be bad since it is shared with the control and the indicator LED.


Edited by LTDteether (10/04/09 10:09 PM)
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#1875589 - 10/04/09 10:19 PM Re: Rear Defrost doesnt work? [Re: LTDteether]
larryo340 Offline
Grand Poobah

Registered: 11/10/08
Posts: 10531
Loc: Long Island
This illustration from the factory manual should help.

Check the main fuse in the underhood fuse panel #14 40amp, and at the underdash fuse panel #17 10amp.

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#1878016 - 10/07/09 06:25 PM Re: Rear Defrost doesnt work? [Re: larryo340]
Kinger87 Offline
Poobah

Registered: 12/15/02
Posts: 7606
Loc: Gladstone MI
thanks for all help so far!!

after further research it appears that the underdash fuse is recieving NO power whatsoever ( on the fuse block itself) . so where do i go from here? does this sound like a bad LCM?
_________________________
"Responding to a question by saying do a search, look in a auto parts catalog, or call a mechanic isn't being helpful"

2001 Crown Vic, Hpp package, air bags n all. stock as can be.


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#1878064 - 10/07/09 07:25 PM Re: Rear Defrost doesnt work? [Re: Kinger87]
LTDteether Offline
Over the Hill

Registered: 07/19/02
Posts: 4446
Loc: Democratic Rep. of Southpaw
Well, I don’t think that fuse will affect the operation of the defroster per se. It appears to protect only the wire to the LED “on” indicator and the wire between the fuse and LED, of course. Does anyone else think that is a weird place to put a fuse?

Kinger, according to the diagram, you should not have power to that fuse unless the circuit is activated, i.e. both the LCM and the under hood fuse are pulled in.

Get to the relay socket under the hood. One control contact on the relay should be hot at all times (black wire). One of the switched contacts gets power from the same circuit (black wire, fuse 14). On the other pin for the control you should get ground after you push the defroster button. If that works, the LCM, the wires between the LCM and the relay and the wire between the switch and the LCM are OK.

If not, check the wire between the LCM and the switch. Get to the LCM connector and check to see if you get ground when you push the button (pin 18). It is probably momentary contact. If yes, the switch and wire are O.K. Move on to pin 12. You should also get ground there if the button is depressed (or you manually ground pin 18) and it is probably supposed to latch. If you don’t see that something in the LCM is FUBAR.

If the relay under the hood is switching, you have coitus interruptus due to a bad element or a wiring problem between the engine compartment and the back window. There are three connectors and one splice between them. #123 sits on top of the HVAC blower motor (it looks like the lower one of two on the stack). #212 is a square one under the pass side if the IP. The last one, 407 is indicated to be on the glass, but the description that I have says it is on the pass side of the luggage compartment.
_________________________
'99 GM GS HPP.
I may not be a rocket scientist, but I *am* a scientist.

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#2653213 - 01/13/13 03:16 AM Re: Rear Defrost doesnt work? [Re: LTDteether]
Calisnowman420 Offline
Member

Registered: 02/07/12
Posts: 138
Loc: Ca
i really need help ima first timer i have a 98 crown vic lx and rear defrost dosent work i checked #17 fuse under dash it was good and check # 14 maxi fuse under hood..,switched relay 1 with relay 2 a and when it was out led for defrost wouldnt comeon but once put back light worked so i believe relays and fuses are all good unless there are other fuses to check ,, i had tint removed from rear window due to peeling and thought that was problem so i had new one put in yesterday and still no defrost i doubt i got a bad window it was carlite but what color should the defrost lines be from inside?..bad lcm the rear defrost is only problem i have besides groan at 13 mph abs check? should relay or something click when pushing defrost button cause led comes on but no click like my honda or my girls camry please help
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98 ford crown vic lx 96,xxx 3:55 truetrac limited slip rearend , kyb gas a just shocks, stock dual exhaust , boc tune

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