View Full Version : rear window defrost


-=79z28=-
12-13-2008, 07:18:55 AM
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.

Gary S
12-13-2008, 09:48:30 AM
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.

tom3
12-13-2008, 11:55:51 AM
Consider a third gen Camaro switch, has the timer built in. Find on Ebay for a few dollars.

rhead007
12-13-2008, 02:34:40 PM
too bad ya wernt closer id give ya the glass from a ta with rear defrogger

-=79z28=-
12-13-2008, 04:31:24 PM
thanks guys, i didnt realize the timer was activated by a momentary switch. this makes it much more simple to me.

79ZED
12-13-2008, 04:54:22 PM
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.

John

Nick Gifford
12-15-2008, 02:47:06 PM
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.

-=79z28=-
12-15-2008, 11:48:12 PM
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.

wow! thanks Nick, that is some great info, i think this is how i will hook it up.