Author Topic: Rear defogger  (Read 1449 times)

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Offline fb_rider

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Rear defogger
« on: April 27, 2007, 10:57:06 AM »
I'm making progress on my rear defogger. I now have it to the point where the led lights up when you turn it on, and it doesn't blow any more fuses. I have one more issue and a question.

The only way that it turns off is by turning off the switch. It does not go off by time, and it does not shut off by turning off the engine. You can't turn it on when the engine is off, but it doesn't go off when you take the key out.

I ordered a new timer, but it came with 5 terminals instead of 4. Does anyone know what the extra terminal is for? Can I use the new timer and leave the extra terminal unused?

Also, the wire at the rear window is not hooked up yet (as I have no tabs at this point to attach it to), but it does have 12 volts when the led is on. Could not having that wire hooked up play a part in the timer issues?
1977 Trans Am SE w/W72 engine (sold)
1999 Trans Am Anniversary Edition #953 (sold)
2000 Trans Am Firehawk #263

Offline ta78w72

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Re: Rear defogger
« Reply #1 on: April 27, 2007, 11:04:48 AM »
Well, you've got a later year timer.  That extra blade is looking for 12 volts.  You should get the four four blade timer.

What year is your car?  If it's a 77 your switch may be incorrect.  Go to Joe Bay's site for the story on this.
http://www.firebirdtransamparts.com/techinfo/harness/optionwire/optionwire.htm#rd

Offline fb_rider

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Re: Rear defogger
« Reply #2 on: April 27, 2007, 11:19:18 AM »
Thanks for the reply.  I already gone through the mid-77 switch issues, which has got me to where I am now (working better than it did before I got the car).  I'm currently using the old timer - I have even tried the new one.  I'm assuming that adding 12 volts to the extra terminal wouldn't allow me to use the new one?  If not, where's a good source to get the correct timer?
1977 Trans Am SE w/W72 engine (sold)
1999 Trans Am Anniversary Edition #953 (sold)
2000 Trans Am Firehawk #263

Offline eroc022

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Re: Rear defogger
« Reply #3 on: April 27, 2007, 11:24:41 AM »
where did you get the timer from?
Eroc
Fixing the car that Restore A Muscle Car jacked up....

Offline fb_rider

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Re: Rear defogger
« Reply #4 on: April 27, 2007, 11:39:59 AM »
Rockauto.com.  Of course, since I took more than 30 days to discover it's wrong, they won't take it back!
1977 Trans Am SE w/W72 engine (sold)
1999 Trans Am Anniversary Edition #953 (sold)
2000 Trans Am Firehawk #263

Offline ta78w72

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Re: Rear defogger
« Reply #5 on: April 27, 2007, 12:57:17 PM »
What I would do is hook up the entire circuit.  I'm not sure what you mean by "tabs"  But the purple wire connects to the green wire near the drivers side kick panel, then travels through the wire tray under the door sill up over the interior rear wheel well hump to the connector on the  rear window.  The other side of the window has a connector which connects to a short piece of braided wire with a loop at the end that fastens to the sheet metal on the rear passenger side of the car (that grounds the circuit).  Once all that is set up correctly, turn on the defogger switch and measure the voltage on the defogger circuit in the back window to make sure you've got current flowing through the window. 

Then see if the timer light goes out after ten minutes.  I'm not sure if the timer works correctly if the circuit isn't fully connected.

As far as finding the correct timing circuit, I'm not sure if they are available.  I have three or four of them because I pull them out of the cars at the salvage yard whenever I find them.  I think I have one or two of the five blade timing circuits too.  I usually don't pull the five blade circuits though because I have no interest in 80 or 81 model years.
« Last Edit: April 27, 2007, 01:01:26 PM by ta78w72 »