W123 Brake light Modification

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Tony From West Oz
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W123 Brake light Modification

Post by Tony From West Oz » Wed 27 Jun, 2007 11:37 pm

I posted this a long time ago, but I feel that now we have a 'How To' page, that I would post a link to it here, so that is more readily found.

W123 Brake Light Modification
This will provide 4 brake lights when you step on the Stop pedal.

Easily done with an additional lamp socket from the light bar from your spare car & a soldering iron.

Regards,
Tony
Life is a journey, with problems to solve, lessons to learn, but most of all, experiences to enjoy.

'83 W123 300D 325000km (Wife's car Josephine - sold).
'84 W123 300D replaced good OM617 912 with OM617 952 and enjoyed having good acceleration for the first time since first driving a 300D in 2002 - became engine and trans donor for 300CD Turbodiesel conversion. Now parted out.
'86 W124 300D sold (Wife's old car - sold )
'85 W123 300CD, 275 000km (Fatmobile) rebuilt turbodiesel from previous Fatmobile transplanted into 280CE (occasional tourer)
'99 W202 C250 Turbodiesel (my darling Wife's car - Sold)
'98 W202 C250 Turbodiesel (my car - Sold)
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Greg in Oz
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Post by Greg in Oz » Thu 28 Jun, 2007 10:31 am

Tony,

I performed a similar mod to my 350SLC many years ago but with the addition of a diode to allow the rear fog lights to still function if required in addition to having four stop lights when the rear fog lights are not in use. The diode (I used one rated at 6 amps) is connected with its anode to the original stop lights and its cathode to the rear fog lights (additional stop lights).

Greg
107023 - 350SLC: 1973, 3sp auto, icon gold, parchment MBtex (sold July 2012 after 29 years ownership)
107026 - 500SLC: 1981, 4sp auto, thistle green, green velour
124090 - 300TE: 1990, 4sp auto, arctic white, cream-beige MBtex
124090 - 300TE: 1992, 4sp auto, malachite (spruce green), black MBtex
201024 - 190E-2.0: 1985, 5sp manual, black, black MBtex
201028 - 190E-2.3 Sportline: 1990, 5sp manual, arctic white, blue leather
201028 - 190E-2.3: 1992, 4sp auto, blueblack, grey MBtex
201028 - 190E-2.3 Sportline: 1990, 4sp auto, signal red, black cloth (parts car)
201034 - 190E-2.3-16 Cosworth: 1985, 5sp manual, blueblack, black leather
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Tony From West Oz
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Post by Tony From West Oz » Thu 28 Jun, 2007 10:16 pm

Even better, add the additional fog light socket and wire both up to the brake lights via a cheap (heat sink mountable) 20A bridge rectifier, screwed to the light bar to absorb excessive heat.
Here is the question, does the W123 wiring harness provide fog light wiring to both left and right light bar connector sockets, or only the right one in RHD countries and left one in LHD countries?

It certainly makes a huge difference to the rear illumination when I hit the brakes.

Tony
Life is a journey, with problems to solve, lessons to learn, but most of all, experiences to enjoy.

'83 W123 300D 325000km (Wife's car Josephine - sold).
'84 W123 300D replaced good OM617 912 with OM617 952 and enjoyed having good acceleration for the first time since first driving a 300D in 2002 - became engine and trans donor for 300CD Turbodiesel conversion. Now parted out.
'86 W124 300D sold (Wife's old car - sold )
'85 W123 300CD, 275 000km (Fatmobile) rebuilt turbodiesel from previous Fatmobile transplanted into 280CE (occasional tourer)
'99 W202 C250 Turbodiesel (my darling Wife's car - Sold)
'98 W202 C250 Turbodiesel (my car - Sold)
'06 Ssanyong Musso Crew Cab 2WD Ute (OM662 diesel and Auto Transmission)

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John Green
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Post by John Green » Fri 29 Jun, 2007 1:36 pm

Here is the question, does the W123 wiring harness provide fog light wiring to both left and right light bar connector sockets, or only the right one in RHD countries and left one in LHD countries?
Only one side for L/H and R/H drive. It needs to be a single light, otherwise it looks like you have your brake lights on.
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Greg in Oz
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Post by Greg in Oz » Fri 29 Jun, 2007 5:01 pm

As John states, there is only one rear fog lamp fitted to MBs, always on the driver's side.

I can't comment on the wiring in the W123, but in my left hand drive 107 (500SLC) the fog lamp wire is only run to the left hand tail lamp assembly. In my right hand drive 107 (350SLC) it runs to the left hand tail lamp assembly in the same way, but then there is an extra wire run separately from the left hand tail lamp assembly directly across to the right hand tail lamp assembly. In this car, by simply fitting the additional fog lamp socket (and pin for the connector) to the left hand tail lamp assembly, I ended up with two rear fog lamps. With a single diode providing feed from the stop lamp wire to the fog lamp wire, I ended up with four stop lamps.

Having only used the rear fog lamps once or twice in the 24 years I have owned the 350SLC, I haven't worried too much about having two rear fog lamps. I also notice that some other makes of car now provide two rear fog lamps anyway. As John says, this arrangement looks like their stop lamps are on all the time. In fact, I find that it is more difficult to notice when the brakes are applied on cars with this arrangement, something those who insist on driving around using their fog lamps should keep in mind (it's also illegal in good weather).

Thinking more about the wiring, if the left hand tail lamp assembly is fitted with the additional stop lamp (in the fog lamp position) wired directly to the adjacent stop lamp, and the right hand tail lamp assembly fitted with a diode feeding its fog lamp from the stop lamp, the result would be just one rear fog lamp as originally intended, but four stop lamps as desired, all without the need for a fog lamp wire to both tail lamp assemblies.

Greg
107023 - 350SLC: 1973, 3sp auto, icon gold, parchment MBtex (sold July 2012 after 29 years ownership)
107026 - 500SLC: 1981, 4sp auto, thistle green, green velour
124090 - 300TE: 1990, 4sp auto, arctic white, cream-beige MBtex
124090 - 300TE: 1992, 4sp auto, malachite (spruce green), black MBtex
201024 - 190E-2.0: 1985, 5sp manual, black, black MBtex
201028 - 190E-2.3 Sportline: 1990, 5sp manual, arctic white, blue leather
201028 - 190E-2.3: 1992, 4sp auto, blueblack, grey MBtex
201028 - 190E-2.3 Sportline: 1990, 4sp auto, signal red, black cloth (parts car)
201034 - 190E-2.3-16 Cosworth: 1985, 5sp manual, blueblack, black leather
YG2S8 - Mini Clubman GT: 1972, 4sp manual, blue, parchment vinyl (my first car which I still own)

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Christo C
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Re: W123 Brake light Modification

Post by Christo C » Wed 16 Jul, 2014 2:35 pm

For anyone interested, similar mod is possible for W124 ( I have 1986 230E) chassis. In this case you will find that Lamp Fail warning will light in dash every time you put foot on brake; the cure is to add another diode - in series with the original Fog wire connected to the Fog taillight: The diode (I used one rated at 3 amps) is connected with its anode to the original FOG light wire and its cathode to the rear fog light, along with the diode from the Brake light.
This prevents the current flowing back up the Fog wire whenever Brake is applied!
~Christo
1986 230E W124.023 M102.982 Thistle Green Saloon "Janis"

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