Troubleshoot/Test Rear Window Defogger?

[scotricker]

I replaced the relay. But the knob still does not light up. It has two detents, I think for low and high power settings. I still do not know if it defrosts at all. Not much humidity around here right now. Can I check it with a volt meter? Is there a tiny bulb in the knob to make it light up? Access to the switch is blocked by dash metal. The radio is out now, but I still cant get to the switch. It's not a big deal, but I would like to make it work. Any suggestions on what to check next?

[86 911 Targa]

Originally Posted by scotricker

I replaced the relay. But the knob still does not light up. It has two detents, I think for low and high power settings. I still do not know if it defrosts at all. Not much humidity around here right now. Can I check it with a volt meter? Is there a tiny bulb in the knob to make it light up? Access to the switch is blocked by dash metal. The radio is out now, but I still cant get to the switch. It's not a big deal, but I would like to make it work. Any suggestions on what to check next?

Our SC is long gone, however:

As I recall, there is a bulb inside the two level switch.

One way to verify voltage to your rear window elements is to put a voltmeter on the rear window wire clips.

There are three on the drivers side under the lower rubber seal.

The one closest to the front of the car is for the upper and lower elements.

The one in the middle is for the center element.

Keep in mind that there are two sets of elements.

1. The center element, which may be for the low setting.

2. The upper and lower elements may be for the high setting.

Was your replacement relay puchased new?

It should look like this.


]



Also, this relay has a "strange" on/off second stage behavior.

Upon researching, I was advised of the following:




Good luck,

Gerry

Is there an SC Bentley?

You may pm me.

[86 911 Targa]

Relay #1 is low setting.

Relay #2 is High setting.

[86 911 Targa]

Here's how it works.

[Stan Gillis]

Where is this relay located?

[86 911 Targa]

Originally Posted by Stan Gillis

Where is this relay located?

Here you go.....

[nineball]

mine have bulbs inside the knobs. they come on with the lights and then get brighter when turned on, or if the lights are not on the knobs are illuminated when turned on.

lights on at night



defrost engaged





i read several posts that talk about the multiple stages of this switch (one pull out for defrost, 2 clicks out for super defrost, rotate to the right for heated mirrors). my switch will pull out but only one click. it does however rotate one click to the right. i am assuming this means i have heated mirrors but not the upgraded rear defrost setting, which seems strange. all the posts i found said that the second pull out (super defrost) was standard but the heated mirrors were an option.

[Stan Gillis]

Thank you for the information and picture on where that relay is located.

[Mike911SC]

Does anyone know what the replacement bulb number is for the defogger knob and the fog light knob? Either the original lamp or ideally an LED.