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Discussion Starter #1
I have a rear window for my 84 Bronco with the defrost grid and a defrost switch that I removed from other trucks (separately). Both look to be in good condition but I want to confirm. I see how to run the test with a multimeter on the grid when it’s installed in the truck, but I would like to test both of them BEFORE I install them (crazy, right?).

For this test I have the items below including the switch, a pigtail plug from the wiring harness, the window (obviously) and a 12v 5amp battery. See picture:

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I am referring to the EVTM for 86 which matches the wiring color scheme from the pigtail I’m using:

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In my mind this should be as easy as hooking 2 wires from the pigtail to the window (1 on each terminal) and 2 wires to the battery (1 positive, 1 ground). Based on the wiring diagram in the EVTM I’m not sure how one would do that. Can anyone explain how to set up the circuit with the switch attached in order to test it? Also, there is another connector that comes out of the switch that isn’t shown on this page of the EVTM. What is that for? Does that need power for the test to work?

Thanks in advance
 

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Discussion Starter #2
Here’s my guess:

Yellow wire and White/Purple wire goes to positive end of battery.
Blue/Brown wire goes to one of the defrost terminals.
Black wire goes to negative terminal of battery.
Other defrost terminal also connects to negative battery terminal (via independent wire).

Am I right?
 

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To test the defrost on the physical window itself you should be able to hook the negative to one terminal of the grid and the positive to the other. That will power the defrost grid. As well as simulate the switch being on. That schematic doesn’t include anything about the switch so I’m not sure on testing that.
 

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1984, 300 L6, smogless, manual 3speed with overdrive.
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Pull a continuity test on the glass if your multimeter can pass power from one side to the other, it “should” be functional if my memory serves me correctly, should be able to test the switch the same way.
 
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