Current Flowing Through Demister/Defogger Switch

[DMC5180]

UH OH, I see there gears turning for another DM-eng product. A simple time-out circuit the protects the whole circuit if the switch gets inadvertently turned ON (which happens a lot) and works like modern day cars.

[Bitsyncmaster]

UH OH, I see there gears turning for another DM-eng product. A simple time-out circuit the protects the whole circuit if the switch gets inadvertently turned ON (which happens a lot) and works like modern day cars.

Not this year. I'm struggling keeping up with what I sell now. My AC panel had to take a back seat to building inventory.

[DMC5180]

not this year. I'm struggling keeping up with what i sell now. My ac panel had to take a back seat to building inventory.

lol j/k

[John Rogers]

I rebuilt my defroster circuit when I installed the window mirror heaters. The new relay-timer switches the heat on for 10 minutes and then switches off permanently. The switch is a momentary switch that can toggle the timer on and off. The light is only on when the defroster is actually heating.

- Click the defroster button to start the timer, light comes on, heating starts
- If left alone, after 10 minutes the defroster switches off, light goes out
- If you click the defroster button while the light is on, the defroster switches off, light goes out

Adding the mirror heaters doesn't complicate the wiring at the relay-timer (but it does mean changes in the doors and behind the rear panels). I also reworked my button panel so that the defroster is a momentary switch.

On the off chance that Dr Jeff still monitors this forum. What did you replace your rear defroster timer relay with? Perhaps a defroster timer relay from a different car. I have a broken window switch that can operate as a momentary switch and a broken defroster switch to donate the rocker with appropriate decal.

[John Rogers]

On the off chance that Dr Jeff still monitors this forum. What did you replace your rear defroster timer relay with? Perhaps a defroster timer relay from a different car. I have a broken window switch that can operate as a momentary switch and a broken defroster switch to donate the rocker with appropriate decal.

I have found a relay that I believe I can wire up to turn off the rear screen defogger after ten minutes. The problem is working out how the old relay is wired so as to be able to rewire it for the new 10 minute timer relay.

There are two wires going to the relay as well as the ground wire. One wire is unpowered and goes to the rear screen defogger. The other wire should be coming from the rear screen switch except that the switch does not interrupt the power as it is continually powered when the ignition key is in the first or second positions. However, if the old green timer relay is in position then the switch does interrupt the power. The wiring diagram shows ground to pin 85, the wire from the switch to pins 86 and 87 and pin 30 powering the defogger.

Does anyone know why the wire from the switch only interrupts the power when a relay is in position?

My alternative solution is to simply run a new wire from the switch to pin 86, move the defogger from pin 30 to pin 87 and plug the continually powered wire into pin 30.

[DMC-Ron]

I have found a relay that I believe I can wire up to turn off the rear screen defogger after ten minutes. The problem is working out how the old relay is wired so as to be able to rewire it for the new 10 minute timer relay.

There are two wires going to the relay as well as the ground wire. One wire is unpowered and goes to the rear screen defogger. The other wire should be coming from the rear screen switch except that the switch does not interrupt the power as it is continually powered when the ignition key is in the first or second positions. However, if the old green timer relay is in position then the switch does interrupt the power. The wiring diagram shows ground to pin 85, the wire from the switch to pins 86 and 87 and pin 30 powering the defogger.

Does anyone know why the wire from the switch only interrupts the power when a relay is in position?

My alternative solution is to simply run a new wire from the switch to pin 86, move the defogger from pin 30 to pin 87 and plug the continually powered wire into pin 30.

John,
First of all I don't haven't worked on the defogger circuit because I've never had a need for the rear window to be defogged. But your description got me curious. I've attached the defogger timer circuit schematic. I've cleaned up the schematic a bit and added a standard auto relay pinout. Assume this were just a standard form C auto relay, When power comes from the defogger switch, it energizes the relay coil (pin 86), relay pulls in and pin 87 is connected to pin 30 and power goes to the rear defogger. I'm speculating here, but I would expect the intended relay to be a special timeout relay, such that if the coil remains powered for a given period of time, the relay contact opens and remains open. When power is removed, the timer resets waiting for coil power to again begin the timeout sequence. If this were a standard form C auto relay the defogger would turn off and on with the switch but it would not automatically turn off after a given period of time. It would remain on until the defogger switch was turned off. If your timeout relay will open the contact after a 10 minutes, then it may work depending on its operational sequence. Would you have a technical sheet on the relay?

RonDefogger Timer Circuit.JPG