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Rear Window Defroster

15910 Views 16 Replies 9 Participants Last post by  whd507
To add to the list of electrical and sensor failures to my Bronco...

My rear defroster doesn't work. When I push the button, the light lights up, but the ice doesn't melt...
Being up in WV, my windows already have a solid sheet of ice on them most mornings (due to ROTC I am up at 0545.)

Any ideas?

Sorry for the massive amount of questions lately, I am still working the bugs out on this thing.:whiteflag
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Wish I could help, but mine doesnt work either. The light on the button doesnt even come on for me. Another little issue I have yet to work on. Considering that I live in Alabama, it hasnt been that high on the priority list.
You'll have to open up the tailgate access panel and look to see if the defroster terminal wires are still connected. If not, you'll have to do some soldering.
Ok I'll have to do that. Never messed with the tailgate before so this will be newish.
I have had 2 back windows replaced due to stupid kids on a B-B gun window shooting spree. Both were changed at local glass shops around here. I found that neither of them worked nearly as good as the original.
mine doesnt work either. keep us updated what you find
I'm in Florida now visiting my parents, I'll be flying back to Pittsburgh this sat. After stopping at Ford to see about the CC sensor recall, I will check out the access panel thing. (Providing I can figure out what I'm doing haha)

I'll report back with anything I see.
mine has a cold spot in the middle. how do i repair that?

hijack over :goodfinge
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All from:
1996 F-150, F-250, F-350, F-Super Duty and Bronco Workshop Manual
Heated Back Window Grid Wire Test

Using a strong light inside vehicle, visually inspect wire grid from outside. A broken grid wire will appear as a brown spot.

Run engine at idle. Set the heated back window switch and light (18C621) to ON. The indicator lamp should come on.

Working inside vehicle with Rotunda Digital Volt-Ohmmeter 014-00407 or equivalent, contact broad (bus bars) red-brown strips on sides of rear window. The meter should read 10-13 volts. A lower voltage reading indicates a loose ground wire (pigtail) connection at grounded side of glass.

Contact a good ground point with negative lead of meter. The voltage reading should not change.

With negative lead of the meter grounded, touch each grid line of heated back window at its midpoint with positive lead. A reading of approximately 6 volts indicates that the line is good. A reading of zero volts indicates that the line is broken between midpoint and the positive side of the grid line. A reading of 12 volts indicates that the circuit is broken between midpoint of grid line and ground

Heated Back Window Switch and Light, Control Assembly Test

Ground Pin 4 and connect a jumper wire between Pins 3 and 2.

Apply power to Pin 2. The indicator should not light.

Momentarily actuate control to the ON position. The indicator should come on and stay on after the control returns to the normal position.

The indicator should go off under the following conditions:

If control is depressed to OFF.
If power to ignition switch accessory terminal is removed or approximately 10 minutes have elapsed.
Apply 12 volts power to Pin 5. The ISO bulb should light.


Heated Back Window Switch Connector, Bronco

Pin Number Circuit Circuit Function
1 186 (BR/LB) Heated Back Window Switch to Heated Back Window Grid
2 185 (BK) Battery Feed to Heated Back Window Switch and Grid
3 8 (O/Y) Heated Back Window Timing Circuit Feed
4 57 (BK) Ground Circuit
5 19 (LB/R) Instrument Panel Lamps Feed
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Thanks for the above info
I'm not one for wires and diagrams and stuff, so I'll look at the whole wire breakage issue and broken spots on the grid. My entire defroster is out, so I'm betting on it being a wire issue.
yo RR,

I hear ya. The kits are a great help.

btw, I posted the other stuff for posterity

It's Fixed!

I took pictures of what i did on my phone... problem is I don't have the card reader with me so I cant upload them till tomorrow.
Basically, the wire in the farthest left side of the window (standing outside of the truck looking in) was frayed and sheared off from the little clip. I cut the end off, stripped it, cleaned the contact points up nicely (found a contact point cleaning kit in the shop, so I used it) and then I added a small amount of solder to help hold the wire to the clip.Then slid the clip over the piece glued to the window, and using a volt meter I checked the entire grid. (after I did the flashlight test mentioned in a write up posted above) (while the switch is on) I clamped the wire to the clip I just fixed and then tested the grid by randomly putting the point on one of the lines. Each time in every location it lit up. Good enough for me. The final test, I turned it on while the truck was running and watched the volt meter. It dropped a little bit, which it did not do before... so I take it I am using power.

No ice build up on the window, so I'll have to wait for that. It's below freezing here, so maybe.

Everything else looked good inside the tailgate. I noticed some moisture in there, but no rust! I also noticed this random screw with the following etched into the metal "Do not removed. "F*&^$d up. This keeps the latch from sticking."

I'll put the pics up later, if anyone wants.
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All from:
1996 F-150, F-250, F-350, F-Super Duty and Bronco Workshop Manual
Heated Back Window Grid Wire Test
yo, This was overwritten in my reply;
Bookmarked for later. You the man! :thumbup
yo Jeff, yw!
Take a look at my site for more info/tech Links on this @
Thanks to Mr. SCHWIM!!

btw, many of your tech stuff is in there; use the Search feauture to see me; type in Iolausthen hit Next Results for more

be well pal!
Well the recent snow fall confirms the fix. Defroster turns ice to running water now.

Spent 0 bucks and about 30 minutes (if that) of time.

Took the ten bolts out to remove the access pannel

This greets me. Frayed and completely disconnected.

Clipped and stripped.

Put back onto the tab,

Put back onto the contact on the window. Put some solder on to hold it in places better. I cleaned up the contact points, they are nice and shiny now.

With the switch on, I'm testing the voltage.

good 'nough for me...
Sorry for the crappy pictures. Cell phone camera... Very low light conditions in our shop at night, and I was using a LED shop light thats too bright for cam purposes. It is also very cold, and the cam lens started fogging.
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I know this is an old thread, but another common issue related to the frayed wire, is that the contact itself gets shaved off the glass. usually on the left side, as there must be something that rubs or contacts that area to fray the wire. there is conductive epoxies available to solve that problem. (Permatex 21351 being one) Both my Broncos have had this issue, and I have seen a few more customers in the store with this issue as well.
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