1978 defroster
Thread Starter
7th Gear
Joined: Nov 2018
Posts: 7
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From: Alabama
1978 defroster
How should the defrost button on a 1978 feel? Mine is springy pushing it forward or reverse and automatically bounces back to center once released.. is this correct? Are there set positions for "on" and "off"? Also, intermittently, it will light up green, but I have yet to see the rear window actually defrost. Suggestions?
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,754
From: Charlotte NC
The switch will spring back into the neutral position due to it is momentary switch. The switch will activate a relay that will supply power to the rear defroster.
If my memory serves me correctly the relay is on a timer (so-to-speak) and it ill shut off when certain parameters are met. So using it in on hot day...it will not work due to it is too hot out.
Do you have a factory service manual for your car????
DUB
If my memory serves me correctly the relay is on a timer (so-to-speak) and it ill shut off when certain parameters are met. So using it in on hot day...it will not work due to it is too hot out.
Do you have a factory service manual for your car????
DUB
Melting Slicks
Joined: Sep 2004
Posts: 3,227
Likes: 671
From: Northeast
78 defogger per chassis manual:
"A control switch activates the system and allows current flow through the rear window grid for approximately 8-12 minutes. A defogger timer, which is also activated when the switch is depressed, automatically shuts off the system. The system can be turned off at any time by momentarily pushing the control switch to the OFF position. The system is protected by a 10amp fuse and a circuit breaker located in the fuse block. "
"A control switch activates the system and allows current flow through the rear window grid for approximately 8-12 minutes. A defogger timer, which is also activated when the switch is depressed, automatically shuts off the system. The system can be turned off at any time by momentarily pushing the control switch to the OFF position. The system is protected by a 10amp fuse and a circuit breaker located in the fuse block. "
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,754
From: Charlotte NC
On your back glass where the grid is there are TWO wires. One on each side. One will be a ground and the other one is the 12 volts that gets turned on when you turn on the defogger.
You can simply test and see if you have a GOOD ground going to the grid...and then also see if you get 12 volts when you turn it on.
Often times I will CAREFULLY remove the power wire and check it when it is disconnected...then attach it and see what happens.
IF you have NO pwoer going to it when you turn it on ....or....you do not have the other wire grounded...ti will NOT work.
IF my memory serves me correctly the wire will be about a 12 gauge BLACK wire with a red or orange stripe of it. If it does that is your 12 volt wire. The wire on the other side will be a 12 gauge SOLID back wire with no stripe on it.
DUB
You can simply test and see if you have a GOOD ground going to the grid...and then also see if you get 12 volts when you turn it on.
Often times I will CAREFULLY remove the power wire and check it when it is disconnected...then attach it and see what happens.
IF you have NO pwoer going to it when you turn it on ....or....you do not have the other wire grounded...ti will NOT work.
IF my memory serves me correctly the wire will be about a 12 gauge BLACK wire with a red or orange stripe of it. If it does that is your 12 volt wire. The wire on the other side will be a 12 gauge SOLID back wire with no stripe on it.
DUB
Last edited by DUB; Nov 23, 2018 at 06:49 PM.
