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post #4 of (permalink) Old 01-03-2002, 07:53 AM
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Re: How to get rear defrost to work on hardtop

Last winter I did a reinstall on my 88 Wrangler defroster . The hardware is pricey from the dealer, which I defaulted to as the Radioshack equipment did not come with the "turn off timer" already built into the relay . The timer is supposed to kill the defrost switch after the first 10 min . and then after 5 min. on subsequent immediate usage. The defrost draws heavy current in the secondary circuit , while only the standard 12v in the primary circuit . Heavy gauge wiring (?) is required for the 20 amp in secondary circuit. Also ,a dash switch is necessary . This usually includes a rocker on/off switch plus an indicator light button ( yellow or orange ). The black plastic dash decal is a dealer item and calls for a dash backlight bulb . I picked up a standard dash backlight fixture with wiring from a salvage yard . Though I used a Jeep source , it looks like almost any lamp socket assembly will work if it can be fitted into the Jeep dash panel near the 'soon to be installed ' Defrost Switch. You can splice the dash lamp wiring into any existing dash lamp wiring . The OEM rocker style Defroster on/off switch ( $35 - $42) is unique in that it has 4 wires . Radioshack had only 3 wires , as did other junkyard switches . The OEM combo timer /relay was approx $35 . Nothing else would substitue completely to fit the dash on/off switch and provide dash lighting and provide a timer function . The aftermarket parts that I found were less $$ but did not provide all features . The thin wiring of the primary circuit runs from the dash to the combo timer /relay and back to the indicato light and the return leg of the switch . The heavy gauge wiring runs from a "fusible 12v link" ( usually red )from battery source , to the secondary circuit of the relay , and then to the rear defroster . Once it plugs into the defroster , it travels through the grids , gets consumed by the resistance in the grid , and then goes to frame ground . Hope this helps.

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