Retrofit 3rd brake light on W124

jeremy156

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My 1993 W124 320E (pre-facelift) does not have a high level brake light fitted.

In considering adding one, I'm aware that the cruise control disengages when the brake light illuminates and as such I'm wondering whether it's a safe bet to simply add an LED brake light in parallel with one of the brake light bulbs, or whether that'll confuse things for the cruise control...?

I'd imagine the N7 bulb-out-warning module probably has a separate output pin for 3rd brake light, which presumably doesn't then relate to the cruise control (big assumption), but I don't know which pin to try and trace a cable path for... and whether it's likely that wire would be in place and simply not used at the rear... or whether I'd need to run a new cable.

Does anyone have a working understanding of the N7 to help me figure this out, please?

Cheers,
Jeremy
 

d215yq

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No idea how the N7 works and but the PO put in a 3rd level brake light in my W124 and wired straight to one of the clusters (forget which one) and the bulb replacement doesn't come on in driving, and did come on when one of the bulbs blew so I'd imagine you's have no problems on that front.

Again no idea how the cruise control works either but I'm guessing it disengages when the brake switch tells it to and it's nothing to do with the brake lights circuit at all?
 
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jeremy156

jeremy156

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Reading around.... the author of (http://www.peachparts.com/shopforum/2591451-post7.html) refers to a dependency on grounding via the brake light bulbs... it sounds like it simply needs at least one bulb to be working to function and that an LED 3rd level brake light in parallel therefore wouldn't hurt.... I will experiment and see...

Meanwhile, does anyone know where to find schematic diagrams?
 

DREAMER NO2

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I would be interested to find out just what type of light the Jeremy will use and the place on rear shelf it will be fitted to .
 
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jeremy156

jeremy156

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OK, tried it and it seems that having a (cheap and nasty) LED array wired in parallel with the feed from a light cluster is fine, the LEDs light quickly, the incandescent bulb still illuminates in the expected time and crucially the cruise control still works.

I'd like to replace the incandescent brake lamp pair with LEDs (for the quicker switch-on), but suspect that would upset the cruise control.... might experiment for amusement...
 

Craiglxviii

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OK, tried it and it seems that having a (cheap and nasty) LED array wired in parallel with the feed from a light cluster is fine, the LEDs light quickly, the incandescent bulb still illuminates in the expected time and crucially the cruise control still works.

I'd like to replace the incandescent brake lamp pair with LEDs (for the quicker switch-on), but suspect that would upset the cruise control.... might experiment for amusement...
Would also be illegal.
 
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jeremy156

jeremy156

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Thought you might say that Craig ;) Presume you're referring to the pair of brake lights.... do you have a view on retrofitted 3rd brake light?
 
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Craiglxviii

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Thought you might say that Craig ;) Presume you're referring to the pair of brake lights.... do you have a view on retrofitted 3rd brake light?
It’s an addition not an alteration, and subsequent model years of your car did have them, so that’s all fine ;)
 
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jeremy156

jeremy156

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Right, so that's key... changing something that was put there my Herr Benz is wrong... but no problem adding something new. Crystal clear, thanks mate. How's little'un?
 

Craiglxviii

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Right, so that's key... changing something that was put there my Herr Benz is wrong... but no problem adding something new. Crystal clear, thanks mate. How's little'un?
He has a cold and isn’t sleeping, so we’re both like the Walking Dead this week!
 
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jeremy156

jeremy156

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Deep joy.... keep your chin up!
 

LostKiwi

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Right, so that's key... changing something that was put there my Herr Benz is wrong... but no problem adding something new. Crystal clear, thanks mate. How's little'un?
The rule is that any light assembly that carries an E-mark must have the appropriate E-marked light source(s).
If you're adding a third light technically it should also be E-marked but it's a little more open to interpretation.
 
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