So my 86 4runner has been at a mechanic for two weeks now (I've owned it three weeks total). Although I'm capable, I had to turn it over so I can focus on my day job.

While it's there I've been thinking about a problem I need to fix when I get it back: the rear defroster button lights up and times out after a while, but I don't get any defrost action on the rear window.

I have new relays for the rear window box (ready to put in) and I'm wondering, if the relay was bad would the button light up or should I start looking into other possible trouble spots? The rig came from So Cal, so I doubt they used the defroster hardly ever - so I'm thinking it's probably not gummed up with carbon

 

The grid is probably shot. I'd put a tester from one terminal to the other on the glass and see what you get (or don't get). My 1973 Datsun still has aworking defrost relays and switches... but man is that grid SCREWED!

Common problem. Electrical grids & coils that get hot on and off over so many years die out. Its the natural way of things.

 

So if it does turn out to be the grid does this mean I need new glass? Is this something windshield shops would carry?

 

Check to make sure the defroster is wired to the glass. My 88 was broken off since it gets weakened from the up down motion. That fixed mine.

 

Finally got around to this amidst all of my other issues. RBX was spot on, the wire was broken off right at the spade connector. It seems to be working now, I just need a foggy or frosty morning to know for sure.

Thanks again!

 

I opened my 86 runner up and the connections had been removed and were very filthy and corroded. A brass brush and some new connections and all appears well, I cut some heat shrink tubing to fit over the connector to ensure they don't become filthy again. I used my electrical tester and it showed a current so we will see if that equates to defrosted window. Thanks guys!!

 

Do you guys have a defogger button or is it just when you flip the aircon to defrost? I've got an '86 22RE 5spd runner

 

the button is for the rear defroster, and the setting on the hvac controls above the radio is for the windsheild. If your is equipped with a rear defroster there will be wires running across the rear glass and a button to the left of the steering wheel to turn it on.

 

I have the lines on my rear window, but I have never seen a defroster button in mine

 

from pictures it looks like I just have a pocket where the button goes, although I know that there are wires behind it. that would explain a lot

 

Maybe someone replaced the rear window with one that has a defroster when yours didn't comes with it. Take the cover off the tailgate and see if its hooked up.

 

Maybe some one can help me. My defroster light comes on, but the defroster doesn't do anything. I took the tailgate apart and here is what I found.
In one picture you can see the wire that isn't attached to anything. In the other you should see the bottom of the rear window where the wire attaches???? How does it attach and is that my problem?

 

Well I figured out the problem I'm pretty sure. In my second picture where I am holding the red cable, there is actually a ground cable that was broken off in that tube as well. I attached both the red and black wire to the tabs that you see on my first picture, and now the voltmeter moves on the dash whenever I press the defrost button. I am assuming the problem is fixed, but I guess I will not know until I actually need the rear defrost. The rear window does not feel warm to the touch when I touch it.

 

Here is a pic

 

Yep, looks like you just fixed it. However, to verify...
(1) Measure voltage between those two wires with button in ON mode and...
(2) with it in OFF mode. Then...
(3) Disconnect the two spade connectors and measure resistance between the pins in the window. There should be some continuity. If not, there might be a break in the de-froster traces. Find it and repair.

 

Thanks for the reply.
Steps 1 & 2 are crystal clear, but step 3 i could use some help understanding.
I have never used a volt meter before...
Are you saying i need to disconnect the two plugs from the window and measure the resistance running through the grid on the window by touching the positive and negative terminals?

 

Correct. Set multi-meter to resistance mode.
I do not have a defroster so I do not know exact resistance to expect but other members may know.

Check this out and other tutorials on multi-meter...
https://learn.sparkfun.com/tutorials...e-a-multimeter

 

Set the ohmmeter to your lowest scale (200 ohms on the Harbor Freight version); you're looking for less than 20 ohms.

Almost anything less than 20 ohms is okay; what you're worried about is "infinite" ohms meaning (most likely) a broken trace on the glass. "Zero" ohms (a short somewhere) would have blown the fuse.

I you have a broken trace, you can get kits with conductive paint to repair it. I've never done it, and I expect it's a fussy job. (you have to remove the clear coat at the break, carefully draw in the new conductive line, then re-clear coat it). But I'm told it will work as a permanent fix.

 

Thanks for the information on fixing the rear window defogger. I followed the suggestions and, like RoBatt, found a broken wire. Following Rad4Runner and scope103's suggestions, I used my multimeter to determine there were no other electrical problems. Once I crimped on a new connector and attached the wire, my defogger is working again.

In case future 4Runner owners with defective rear window defoggers are unfamiliar with the procedure, I would add that one should "trick" the system into believing that the tailgate is closed and locked by closing the tailgate latches when it is open. Thereby, the rear window can be raised and lowered to give access to the electrical attachments for the defogger.

 

If that female spade plug fixed the problem, then I'd disconnect it, slide a section of shrink over and past it, reconnect the plug, slip the shrink tube over the whole connection to seal it for good. My OCD makes me do stuff like that.