rear window defrost

Discussion in 'Electrical Systems' started by -=79z28=-, Dec 13, 2008.

  1. -=79z28=-

    -=79z28=- Veteran Member Lifetime Gold Member

    Jan 22, 2008
    Charlotte, NC
    i was thinking about getting a new rear windshield in the future, and i really would like to have electric defrost on it if i replace it. my car did not come with electric defrost, and i was wondering (since my dad will end up making a complete new harness for the car anyway) if i could run a switch and relay only on when ign. circuit is on to the defroster. is this a safe way? is there a better way? is there a way to do it with a timed switch? my dad said the reason they have a safety timer from the factory is because they would crack windshields if they were left on too long.
  2. Gary S

    Gary S Administrator Lifetime Gold Member

    Apr 14, 1999
    Bismarck, North Dakota
    You could buy the factory timer unit and a momentary switch to activate it. If you add the wiring yourself, you can run it through a relay so that there is no power available for it unless the ignition switch is on.
  3. tom3

    tom3 Veteran Member

    Aug 1, 1999
    Consider a third gen Camaro switch, has the timer built in. Find on Ebay for a few dollars.
  4. rhead007

    rhead007 Veteran Member

    Oct 25, 2000
    too bad ya wernt closer id give ya the glass from a ta with rear defrogger
  5. -=79z28=-

    -=79z28=- Veteran Member Lifetime Gold Member

    Jan 22, 2008
    Charlotte, NC
    thanks guys, i didnt realize the timer was activated by a momentary switch. this makes it much more simple to me.
  6. 79ZED

    79ZED Veteran Member

    Jan 31, 2000
    Nanaimo, B.C., Canada
    If you don't have the rear glass, you'll have to scrounge around for a used one. At the present time, the backlight glass with the electric defogger grid is not being reproduced.

  7. Nick Gifford

    Nick Gifford Veteran Member

    Aug 10, 2000
    Chelmsford, England, UK
    The 79 factory harness took a big guage orange/black power feed that ran to the relay from the top left of the fuse box next to the power accessory circuit breaker (same place that might feed power windows). There was an additional split wire to a spare outlet wrapped in the harness near the steering column in slightly smaller guage for other power accessories.
    The relay was mounted to the dash bracket that supported the side of the ash tray/ radio. The ignition feed was the usual purple/white also with a spare feed.
    The rocker switch in the dash was self centering, with a small green led in the middle to signify it was on. So when you pressed the rocker up, the led would come on and the switch returned to the center position by spring pressure. To turn it off, you pressed down on the rocker, or you left it and the green light would go out on the timer.
  8. -=79z28=-

    -=79z28=- Veteran Member Lifetime Gold Member

    Jan 22, 2008
    Charlotte, NC
    wow! thanks Nick, that is some great info, i think this is how i will hook it up.

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