Rear Defogger

[sperold]

It is time to use the rear defogger again.
I have a variety of dash switches, but none of them seem to do the job. It is hard to believe they are all bad so I could use a little background.

Does the switch have the small indicator light in it that lights up when the circuit is complete?

Is there a way to test the switch when it is out of the car?

Is this set-up like the fog lights where there is a relay buried under the column somewhere that has to be considered too?

Can the rear defrost be activated in run and accessories or just run?

It has some kind of a timer built into it, how does that work, and is it a source of problems?

 

[rubydist]

yes, there is a relay with a timer - you turn it on and it automatically goes off after a pre-set time period. It draws a lot of current, so I believe it only works in "run" position. iirc, there is an indicator somewhere, but I don't remember if its in the switch or on the dash?

 

[sperold]

Has anyone ever spotted this relay with a timer in their under dash adventures.
I know sometimes these things show up in different places, depending on the build date.
Mine is a June 95 MTX if it matters.
What colour is it and what does it look like?

 

[tompumped]

I don't remember, but I think it's on the passenger side. All you have to do is have someone push the button and start looking. There's a bulb in the switch.

 

[sperold]

I am starting to think everything is contained in that push button switch just to the left of the speedo area (1995).

I viewed an old 1990 Helms manual and there is a Section 38-86 Window, Rear - Defogger that shows all the important functions inside one dotted enclosure. That makes me think it is all contained in that odd shaped push button switch on the dash.

Has anyone ever changed anything other than the dash switch to fix the rear window defogger?

 

[luigisho]

Only silver conductive adhesive to reattach a loose contact or connect broken defrost lines on the rear glass.

 

[sperold]

I took the dash mounted push button switch apart. There is a printed circuit board with a rather large relay or something mounted on it.

The switch comes apart from the back where the wire connector fastens, that small extension comes off the case with a little prying. Then you have to take out the circular white light on the side of the case by turning it 90 degrees and prying it out with the small jewellers screwdriver. Then the circuit board slides out while the push button part stays in the overall case.

I shined the contacts on the little relay part and shined up the connector prongs and put it back together.

I will try it in the car when I return after the weekend.

 

[luigisho]

Have you tested to make sure power is going in to the switch and checked to make sure there is nothing going out?

 

[itwonder]

FWIW, here's the wiring diagram from the FSM: