Author Topic: Wiring Instructions for Hardtop Rear Defrost Switch  (Read 307 times)

Walter Marsh

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Wiring Instructions for Hardtop Rear Defrost Switch
« on: January 11, 2019, 17:29:28 »
Hello Pagoda Group,

I’d like to thank all those members below who kindly responded to my post.  In addition to those, who have further assisted me in my restoration endeavors.  So, I figured, I should at least extend the courtesy and offer a correction on how to install a "Heated Rear Window Defrost Wiring Harness" according to Mercedes-Benz factory specifications.

In full disclosure, this post initially began several years ago when I was trying to remember how this original wiring harness was routed along the interior contours of my vehicle. Since then, I’ve made great progress with my 7 year, 280S - Bolt & Nut Restoration.  I am literally at the end of the tunnel and can hardly wait to drive her. Just buttoning up the last loose ends.

*PLEASE NOTE:
A TRANSLATED COPY OF MERCEDES-BENZ  FACTORY TECHNICAL MANUAL ADDRESSING & ILLUSTRATING THIS TOPIC IN GREATER DETAIL IS AVAILABLE UPON REQUEST.


HEATED REAR WINDOW WIRING HARNESS
The "Heated Rear Window Wiring Harness" sometimes referred to as the “Defrost Wiring Harness” is considered Special Equipment in Mercedes Benz technical manuals.  According to Mercedes-Benz there are two version of heated glass available; composite safety glass (Sigla) and Laminated safety glass heat-insulating (embossed, Sigla). And, depending on the manual, they may be referred to as an Additional, Auxiliary or Supplementary harnesses.  (Note: For the remaining purposes of this Topic we will refer to the "Heated Rear Window Defrost Wiring Harness" as the “Harness").

CONSTRUCTION & COLOR CODING
The construction of the “Harness" is depicted in (Fig. 1 of 3) provided below.

ROUTING & INSTALLATION
The routing of the “Harness” is depicted in (Fig. 2 of 4) provided below.
The “Harness" connects to the vehicle at a total of (6) locations.
(Note: There is no timer relay in its original configuration - that feature was installed on other Mercedes models.)

It is not definitively clear which Fuse No. the “Harness” is connected to at the Main Fuse Panel.
Ostensibly, there are only two viable choices either (Fuse No. 2 or No. 6) since they are the only positions which contain 25A fuses on the main fuse panel.  This is further supported by the BBB service manual which mentions the supplementary fuse box for options such as the “Heated Rear Window” requires (16A) and may be confirmed in (Fig. 3 of 3 ) or on (Pg. 15 . 54 . 82-0/5 of the BBB).

For all intents and purposes, I connected my “Harness" to the Main Fuse Panel at the former rather than latter position and connected to ground at the inner dash "ground spot" directly behind the dash to the lower right of the speedometer and lower left of the radio.

The “Harness” additionally connects to the Supplementary Fuse Box within the engine compartment to the left of the Break Booster. This connection requires a Red (16A) Fuse, preferably copper. 

The perpendicular portion of the “Harness" then runs down the back of the firewall over toward the heater blower motor on the drivers side footwell and down along the transmission tunnel anchored in place with aluminum tape so as to not interfere with carpet installation. 

It continues down along the top lefthand side of the transmission tunnel passed the emergency brake (checking for proper clearance) and 1/4” to the left of the shift gate with just enough harness so that 4-pole connector can be easily be connected to the switch mounted in the center wooden console. 

From there, the harness continues along the center tunnel toward the back of the vehicle and down to the floorboard traversing behind the driver's seat again as illustrated by (Fig. 2 of 4).  Once more, I anchored the “Harness” in several place along this path until it reached the far most left rear corner of the floorboard. It then climbs up to the sill and into the B-Pillar Box following the main rear wiring harness. 

From there the “Harness” is pushed thru the hole behind the upholstered of B-Pillar panelling and the remaining 2-Gang connector is installed so as to properly connect to the Hardtop’s 2-Gang coupler.

Finally, carpet is installed over the wiring which provides additional anchoring.

OPERATION 
The switch is manually controlled either by pulling-Up for “ON” or Pushing-Down for “OFF”.
Note: This means it will remain engaged until manually shut-off since it is not connected to a time relay.
« Last Edit: Today at 01:59:43 by Walter Marsh »

Pawel66

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Re: Wiring Instructions for Hardtop Rear Defrost Switch
« Reply #1 on: January 12, 2019, 22:51:30 »
Walter, I found it in the BBB, page 15-54-82-0/5, (for /8 cars, as of 1968), under the fuse designation table:

"... The supplementary fuseboxes for options, such as electrical operation of sunroof (25A), heated rear window (16A), electric window raiser (4x25A) etc. are in the engine compartment."

So there it is. I will try to find if this is the fusebox that is next to brake booster or some other one.

I will have to re-do my installation...
Pawel

280SL 1970 automatic 180G Silver
W128 220SE
W121 190SL
G-class

Pawel66

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Re: Wiring Instructions for Hardtop Rear Defrost Switch
« Reply #2 on: January 12, 2019, 23:50:46 »
Walter, just to add confusion. I checked the documentation made by the gentleman who was doing my harness (attached). It looks like he just had this and other descriptions on his files.

Here I think he may be giving the PN for the harness (but EPC does not recognize the number, so I could not verify it). It says power is supplied from fuse No. 2, which is something different than what the BBB is saying or at least so it seems.

I need to check what I have in the car - I recall fuse 6, perhaps my mechanic confused it...

I do not know if I am helping here...
Pawel

280SL 1970 automatic 180G Silver
W128 220SE
W121 190SL
G-class

mbzse

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Re: Wiring Instructions for Hardtop Rear Defrost Switch
« Reply #3 on: January 13, 2019, 16:19:36 »
Quote from: Pawel66
Perhaps .../... there is a detailed description of the rear heated window option.../...
This is the cable routing sketch from M-B
« Last Edit: January 13, 2019, 16:23:45 by mbzse »
/Hans S

Pawel66

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Re: Wiring Instructions for Hardtop Rear Defrost Switch
« Reply #4 on: January 13, 2019, 16:34:34 »
Hans, thank you!

I think this is what Walter, and then me, were looking for!

So it goes from fuse box, to the additional fuse box (I think the one next to brake booster) and back inside.

There is no right hands side part of the T (it is there in my car...need to check what it really is).

Question remains from which fuse it is powered. On the sketch from the electrician I had fuse 2 output. BBB says this circuit requires 16A, only fuse 2 and 6 are 25A, rest is 8A. So if it is an output side, it probably is one of these 2. Unless it goes from one of the fuses input, since the circuit is fused anyway. That I do not know...
Pawel

280SL 1970 automatic 180G Silver
W128 220SE
W121 190SL
G-class

66andBlue

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Re: Wiring Instructions for Hardtop Rear Defrost Switch
« Reply #5 on: January 13, 2019, 20:07:21 »
I am specifically seeking answers to the following questions...
Q1: At which Fuse No. did the factory connect the harness to draw it power?
Q2: Where do the two (Red/Black) wires with eyelets which run across the dashboard air distribution box behind the glove box terminate?
Walter,
the MB instructions indicate that the + (black/red) wire goes goes to fuse 2 and the - ground (brown) to the main grounding point underneath the instruments. See attached diagram.
Alfred
1964 230SL manual 4-speed 568H signal red
1966 230SL automatic 334G light blue (sold)
1968 280SL automatic (now 904G midnight blue)

Pawel66

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Re: Wiring Instructions for Hardtop Rear Defrost Switch
« Reply #6 on: January 14, 2019, 09:49:55 »
I was also very keen on solving this - thank you Alfred, thank you Hans!

Now, if you were doing it yourself - would you hook the wire to fuse no. 2 in or out connector?
Pawel

280SL 1970 automatic 180G Silver
W128 220SE
W121 190SL
G-class