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1973 450 SL
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Discussion Starter #1 (Edited)
R107 instrument clusters prior to chassis number 014754 have a different housing and warning light panel than later versions. The lens covering the warning lights is one piece of plastic, prone to crazing and cracks. This lens is NLA. I have been through 2 replacements from salvage and the appearance of the instrument cluster has bothered me for 10 years. This is not my cluster but it does have my original warning light lens installed.

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Starting at R107 chassis number 014754, the housing changed. The most obvious difference was a tachometer that included a clock. W116 made this change at chassis 000100 (late 1972). My theory is that the big sedan needed more climate control air flow from the center vent area which forced removal of the Kienzle clock from that location to the instrument cluster. The R107 followed suit several months later, probably due to cost savings achieved by parts commonality.


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Focusing on the warning light panel, notice the relocation of the lights. Also notice the change in thickness of the housing area below the warning light panel. This housing fits the dash opening of the W116 perfectly. A supplemental "frame" (MB A1075420087) was fitted below this housing to fill the gap in the R107 dash opening.

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The location of the warning lights in our instrument clusters is governed by the connector plate (circuit board) used to mount the instruments. Early clusters had connector plates for the triple gauge and the early tachometer. The body harness for these cars has 2 connectors for the cluster.



Later clusters have a single connector plate for the triple gauge - electrical items on the tachometer side were wired peripherally. The body harness for these cars only had one connector for the cluster.

 

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'79 450SL, '04 CLK200 convertible; former A124, W210, A209.
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Great write up Brad, very interesting - thanks for taking the time to share this! I always thought that the clock in the center vent was avant-garde in terms of design, and I never really understood why it was moved to the cluster.
 

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1973 450 SL
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Discussion Starter #3 (Edited)
VDO made our instrument clusters. Both housings discussed above accept gauges from the entire production of R107 and W116 vehicles. A recent salvage of a 1973 450 SE produced an instrument cluster with a later version housing and a nice warning light panel. I used this cluster and several other salvage units to see if I could put together an instrument cluster that looked better in my car.

A closer look at the warning light panel can be made by removing the gauges and separating the inner housing section. The early warning light panel single piece lens was mounted with screws.

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The later version housing has a 3 piece lens set. The plastic is thicker. The warning light pieces have a 90 degree profile that enable them to be mounted into slots extruded into the housing. Notice the housing fittings for the odometer and lighting rheostat knobs. Also notice the additional knob for the clock adjustment.

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These warning light pieces are still available from parts suppliers. The one on the left is A0005400643. A replacement part A1165401443 has the same layout but replaces the brake symbol with "BRAKE". The piece on the right has a lot of possible part numbers. ABS, Fasten Seat Belts, O2 Sensor and others with various symbols joined the right turn signal over the years. This part is generally more expensive and difficult to determine which part number you need. The piece in the middle has nothing embossed on it. A Styrofoam block with black paint on the forward edge fills the void behind it. An LCD would fit nicely in this position - maybe an idea for a later project.

Using the new warning light pieces requires the later version housing (MB A1075420056). The location of the lights requires using the connector plate of the triple gauge of the later version housing (MB A0005421778). I wanted to keep my early tachometer without the clock because I've spent a stupid amount of money making the Kienzle clock in the center dash of my car keep perfect time. I did some bench work with a salvage combination of gauges that made steps toward this goal. In the end, I came up with a solution that involved building up an adapter harness to mate this new cluster to my body harness.

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Before I get into detail on this adapter harness, I should explain a few more challenges. The Hi Beam light and Battery/Charge light are relocated with this new cluster housing. The old tachometer has its own connector plate with these circuits on it. It also has circuits for the right turn signal and the dimmer rheostat. I had some duplication to eliminate:

1. Replace the leads for the Hi Beam and Battery lights from the old tachometer to the new triple gauge.
2. Eliminate the peripheral lead for the right turn signal from the new triple gauge.
3. Eliminate the power lead for the dimmer rheostat from the new triple gauge - use the old style rheostat which is powered from the old tachometer connector plate.

The attached "Instrument Cluster Study.pdf" goes into detail about the electrical pin out of these clusters. I'll spare the casual reader and continue to focus on the big picture in the next post.
 

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1973 450 SL
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Discussion Starter #4 (Edited)
One compromise of keeping my old tachometer (without the clock) in the new cluster housing which includes a provision for a clock adjustment knob is dealing with the unnecessary hole in the cluster housing. The options were to fill the hole with some type of plug or retain the clock adjustment knob and make it non functional. I chose the latter and will keep my mind working on the plug option.

I removed the entire clock adjustment mechanism from the tach/clock of a salvage cluster. Next, I removed the adjustment stem. To prevent interference with the old tachometer body, I cut the stem and mounted the resultant assembly inside the new cluster housing.

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Another idea for a future project - use this location to mount a control for an LCD display in the center (dead space) position of the instrument cluster. I'm not a big fan of over modernizing a classic Mercedes-Benz, but I do like discrete modifications that can be easily removed.

The pins on the connector plates of these VDO instrument clusters are 2.5mm, in common use throughout the MB line in later years. Kroschu made the connectors and the body harness. The female connector plugs have a locator that matches a shape in the middle of the pin ring which keeps the circuits wired correctly. Early clusters with 2 connector plates had a half-moon locator on the tachometer and an isosceles trapezoid shaped locator on the triple gauge.

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Later version clusters with the single connector plate on the triple gauge had half-moon shaped locators.

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My adapter harness required two half-moon locator plugs to mate with pictures 1 and 3 above. I used salvage cluster plugs to assemble this side of the adapter harness. The next challenge was to build a secure set of connections for the body harness side. After a few hours of experimentation, I decided to cut the pin rings out of connector plates from from other MB clusters that had pin population matching my needs. One came from a W201, the other from an old W115. Both pin rings had half-moon locators. I sanded these rings down to a point where I could get a harness boot around them then soldered up the correct colored leads to the back side of the pins.

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The body harness of my car, with 2 connectors had plugs that looked like this to match the early style cluster connections.

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Like all Kroschu connectors, the caps of these female plugs can be removed and replaced. Since my adapter harness has half-moon connectors at all 4 connection points, I had to replace the pin bushing cap on the left above.

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After replacing the cap on the left, my adapter harness could be connected to the body harness.

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1973 450 SL
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Discussion Starter #5
After a bench test, I decided to pull the cluster from my car and install my speedometer and tachometer (without clock) in this new cluster. I also polished up the best gauge lens I had on hand and installed the spacers around the edge (commonly broken and/or missing). My wife re-painted the needles on these gauges after practicing on some gauges that I don't care about. Visually this new cluster was ready to install for a test. I setup the adapter harness and plugged it all in. I had good results until I noticed a fuel gauge that was not working. I did a continuity check - my adapter harness was good, the W116 fuel gauge was dead. Out came the cluster for some more work . . .

If you take a look at the connector card of a triple gauge from these instrument clusters, you will notice there are screws and nuts on the back which hold the triple gauge to the connector plate. When these are removed, you can press the triple gauge off 4 electrical pins and separate the actual gauge part from the circuit board. I did this to replace the W116 triple gauge from the W116 connector plate with the triple gauge from my original instrument cluster. In summary, all my original gauges are installed in a new version housing with a new version connector plate behind the triple gauge. My adapter harness and a half-moon cap for the left side plug are installed to make my car talk to this cluster.

All this was done to remove the eyesore of a crazed, cracked lens on my warning lights. The entire effort was made under stay at home orders by the Governor of New Mexico during the COVID-19 pandemic of 2020. I listened to hours of talk radio as I worked. I have ordered MB part A1075400087 (spacer frame below the cluster) to fill the gap in my dash opening below this cluster. All circuits are working well in the car. I am waiting to get a low fuel state to see the low fuel light illuminate - it worked on the bench but I want to see it work in the car.

I have another idea for a discrete modification to this cluster. I am studying the Ford-Philco tempomat system in my car to see if I can build a circuit that illuminates a light in the empty green position of the right side of my cluster. I do not intend to place a symbol on the lens - just a green light when my cruise control is engaged.

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1989 560SL
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Wow!! What an excellent write-up and such detailed research and diagrams. Hats off to you.


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1974 450SL (US), 2005 SLK200 (UK)
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The green turn signals were faded on mine. I slid some pieces of clear green Avery divider plastic in. $5 repair. For the needles I used Walmart Folk Art Neon Orange paint - $1. Both of these were from recommendations on here. Andy
 

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1983 380SL, 2000 S430, 1991 420SEL (retired) - RHD
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The green turn signals were faded on mine. I slid some pieces of clear green Avery divider plastic in. $5 repair. For the needles I used Walmart Folk Art Neon Orange paint - $1. Both of these were from recommendations on here. Andy
I put green LED's in mine so I could see them more easily in daylight
 

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1976 450SL
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I see the comment about adding an LCD display in the slot below the instruments. I've seen an LCD temperature gauge that fits in this spot (it was for sale on Ebay a couple of years ago) - I think it came from another model of MB.

I am interested in anyone who's done anything useful with that area - it definitely makes a suitable place for a display of some sort, and with a darkened screen would be invisible if not powered up. I had considered modifying a Bluetooth adapter, but in the end opted to fit that in the spot originally occupied by the ashtray.
 

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'79 450SL, '04 CLK200 convertible; former A124, W210, A209.
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Super thread - added to favourites and should be linked to EGV. Thanks Brad!
 

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1985 380sl
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All this was done to remove the eyesore of a crazed, cracked lens on my warning lights.
Amazing!!

I have another idea for a discrete modification to this cluster. I am studying the Ford-Philco tempomat system in my car to see if I can build a circuit that illuminates a light in the empty green position of the right side of my cluster. I do not intend to place a symbol on the lens - just a green light when my cruise control is engaged.
I love the cruise indicator concept. If you should decide to place a symbol or text on that, I could use my graphic design powers to generate a period-looking icon or text so it looks like the Germans did it in 1974. My dash has a few indicator lights with text that we could match with the correct font/size. Could be accomplished via something like this dry transfer option that looks pretty durable. DecalProFX | Dry transfer decals in 8 min Just an idea.
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1973 450 SL
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That area below the dials was the ugliest thing about my car when I got it, the clear plastic was crazed and faded and the unused spot's blanks had bleached out and were this ugly tan color. I didn't go to nearly the effort as the OP but I did take it all apart, clean it, polished all the clear plastic and re-did that lower indicator area.
Before:
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After:
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Discussion Starter #15
Please tell us how you got rid of the crazing by polishing that piece. You also did some creative work remaking those symbols - how was that done?
 

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1973 450 SL
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Please tell us how you got rid of the crazing by polishing that piece. You also did some creative work remaking those symbols - how was that done?
Much the same way one fixes headlights. I had to get pretty aggressive with them, 2 stages of wetsand paper then lense polish and they were crystal clear again (lens polish only on the dial windows). This of course removed the symbols. Since I wasn't worried about strict originality I found generic symbols on-line and had my wife cut them out of white vinyl on her Cricut. My placement wasn't absolutely perfect as you can see so the next time I take that out (I still have backlight issues) I will redo them.
 

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Discussion Starter #17
Got it - I have another project. I may end up back where I started because I'm having a tough time finding the spacer frame that goes below the new style instrument cluster (MB part 1075420087). Many places claim to have it but don't actually have it.

@joser85 has very strong Kung Fu in the graphics design world. I will attempt to polish the OE one piece lens and consult him afterwards.
 
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