Rear Window Defrost Switch

[Lars G]

Hi,
 
For the moment I am strugling with the knob for the hardtop´s rear window defroster! I have pulled, I have tryed to unscrew it, nothing works!
How should it be done? Does anybody know?

Br
Lars

[waltklatt]

Dies it have a light that comes on when activated?
It should unscrew from the shaft.
Twist in a counter clock wise motion.
No worries if it breaks.
I have two spares here.
Thanks,
Walter

[mmizesko]

Lars,

If you are asking about the operation of the switch, the knob pulls up vertically to the on position, approximately 1/2 inch.  There is a small light bulb under the white dot in the middle of the knob which illuminates when on.  To turn off, simply push down on the knob. 

There is a timer relay in the circuit for auto shutoff after 10 minutes or so in the w108 sedans, but I haven't been able to find it in the original wiring in the w113. 

Does anyone else know about the timer relay in the roadster?  I'm putting wiring in my 1970 280SL to accommodate my hardtop(with defroster from a 1971) , and the wiring I found from a 113 does not have the relay, but the similar wiring from a 108 does. 

Any help would be appreciated.

Mike Mizesko
Columbus, OH

[tel76]

Mike,
There was no relay fitted to the car or associated with the wiring harness that i sent you.

[mmizesko]

Eric,

I understand completely.  I was just wondering how the switch worked without the relay.  Was it always on until pushed back in?  Will it be safer with the 108 timer relay put in?  Just wanted to understand the operation from a 1970 1/2 to 1971 hardtop defroster user.

Mike

[scoot]

My understanding is that there are two different "defrost switch" setups, both have the same knob with the white dot that gets illuminated.

Type 1 is a momentary switch that toggles a relay. 
Type 2 is a pull on push off switch that has no relay involved.

My 1971 250C W114 coupe had the type that you pull on and push off.  I'm not familiar with a car that has the momentary switch with relay.  Having said that, I would think that if you have the wrong switch nothing is going to work right.   I can check when I'm at home (I'm on travel) for number of contacts on type 2 switch but I would think it would be two contacts, and on momentary switch I would think it would be 3 contacts.

Scott

[mmizesko]

Scott, I have the three prong switch, but it is mounted in the switch holder that goes behind the ashtray, so I thought it was out of a 113. 

I have the 108 and the 113 wiring. 

The 113 wiring has 2 wires in and one wire out on the switch, and the hot goes back to the B pillar and joins with a ground to chassis at the female plug for the hardtop.   

The 108 wiring looks like three wires in, a hidden bundle to the relay, then two back to either side of the fuse panel, and one hot back to the defroster.

I think I'm going to let Joe A have a look.

Scoot, I guess I agree with you about the switch.  I look forward to your follow up.

Thanks,

Mike

[ctaylor738]

Mike,

A relay whether timed or not is a better solution than running the primary circuit through the switch.  The timer relay I use on my Hot Start Solution would work very well.

http://www.sl113.org/forums/index.php?topic=17329.0

Cheers,

CT

[Lars G]

It was impossible to get of the knob in one piece. The old plastic sheared of the nut so I have to find a new knob. The insert was cracked since before and the white dot was completely dried and broken. The nut was so stuck that I had to cut it with my Dremel!
Thanks  /Lars

[scoot]

It was impossible to get of the knob in one piece. The old plastic sheared of the nut so I have to find a new knob. The insert was cracked since before and the white dot was completely dried and broken. The nut was so stuck that I had to cut it with my Dremel!
Thanks  /Lars

Wow.   How is the rest of the car in terms of rust and damage...?