I have a burned out brake light bulb, but I can't see how to access the bulb/s. I found photos of the proccedure on a sedan, which looks straightforward. On my wagon, though, it looks completely different. I must be missing something, no? This shouldn't be a difficult job, but I don't see how to get in there...

On mine, one side has a weird style of bolt with a slot you can use to unscrew it using a screwdriver and the other side has nuts. Access is from the inside.

Easy-Peasy :

Remove the inside trim panel on the side you need to access, if the driver's side you'll need to remove the spare tire as well, look for the two slotted screws and undo them, GENTLY pull the rectangular bulb holder free and carefully remove the old bulb, wipe the side contacts where the bulbs pins go and insert new bulbs ~ I use LED's in all three, much safer and so on .

LOOK CLOSELY at the other bulbs if you see any shiny haze or black inside the globe, that bulb is near death, replace it now .

The black plastic rectangular bulb holder is really easy to damage so BE GENTLE with it .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Does changing the brake light bulbs to LED's affect the cruise control?

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

These are the type of questions you will only see on an old mercedes forum lol...

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[EDIT: An LED probably won't have the same resistance as a light bulb. It will look like an open circuit / bad bulb to things like a cruise control or blinker relay. If you find for yourself that it doesn't, below is a recipe for a modification that will make the circuit look the same to the cruise or blinker system. Since this details a modification to a vehicle safety system i'm gonna recommend caution, common sense, and advise that I don't take responsibility for problems that result.]

To match the resistance of an old brake light or blinker bulb with an LED (assuming it isn't matched already), you can put a resistor in parralel with the LED.

1. Determine the current draw (I) of the old bulb (use a multimeter in series or a clamp current meter) and voltage drop across (V) it (multimeter)
From Ohm's law: V=IR, with algebra, R=V/I

Or use this:
https://ohmslawcalculator.com/ohms-law-calculator

1a. Same for the LED.

2. If the LED resistance is higher (probably is by a lot) then connect a resistor in parallel with the LED (or the hot and ground of the lamp socket)

Use this or a similar calculator so the resistance of the LED/resistor combination matches the resistance of the original light bulb:
https://www.allaboutcircuits.com/tools/parallel-resistance-calculator/

To calculate the power the rating for the resistor using (P)ower, and (Voltage):
P=IV, where I=V/R, P=V²/R

Or just use this.

https://www.amplifiedparts.com/tech-articles/resistor-power-rating


With a resistor in parallel, the load that the cruise control or blinker relay sees will be the same and the CC or blinker relay should be happy about that and work as designed.

Cautions:
Observe all relevant cautions when altering vehicle wiring and safety systems. Use good practices when making electrical connections and test the result. This information is offered without implied or explicit guarantee of correctness, legality, appropriatness or safety.

Finally: PLEASE USE CONSISTENT AND APPROPRIATE UNITS THROUGHOUT YOUR CALCULATIONS, AND ENTER NUMBERS CONSISTENT WITH THE UNITS WEB OF ANY CALCULATORS YOU USE. GARBAGE IN = GARBAGE OUT.

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CC: NSA

All things are burning, know this and be released.

82 Benz 240 D, Kuan Yin
12 Ford Escape 4wd

You're four times

It's hard to

more likely to

concentrate on

have an accident

two things

when you're on

at the same time.

a cell phone.

www.kiva.org It's not like there's anything wrong with feeling good, is there?

I suppose I should have asked this in a different way.

Does changing the brake light bulb to an LED, which has a lower resistance value, affect the function of the cruise control's release when applying the brakes?

The lecture on Ohm's Law was nice but did not answer the question. There are too many variables in the system's circuit (age of wiring, corrosion, etc.) to accurately estimate the true resistance either required by the system or existent.

A "yes" or "no" answer would be much more useful to a future reader of this forum.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

What Moon was trying to say is that unless the LED light bulb you install has a loading resistor, it will screw up your cruise control. If the LED doesn't have a loading resistor, you can calculate the value you need and add it across the LED.

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Current stable:
1995 E320 149K (Nancy)
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Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

LED's also make your blinkers blink fast unless you put a resistor across them.

__________________
CC: NSA

All things are burning, know this and be released.

82 Benz 240 D, Kuan Yin
12 Ford Escape 4wd

You're four times

It's hard to

more likely to

concentrate on

have an accident

two things

when you're on

at the same time.

a cell phone.

www.kiva.org It's not like there's anything wrong with feeling good, is there?

And LED's have a higher resistance, that's why they use less current and less power. They look like an open circuit to the flasher relay and the blinkers cycle fast like when you have a burned out bulb on your blinkers.

__________________
CC: NSA

All things are burning, know this and be released.

82 Benz 240 D, Kuan Yin
12 Ford Escape 4wd

You're four times

It's hard to

more likely to

concentrate on

have an accident

two things

when you're on

at the same time.

a cell phone.

www.kiva.org It's not like there's anything wrong with feeling good, is there?

Meant to say lower voltage requirement.

Trying to type while fending off a sixty pound dog who is convinced he is still a puppy who can fit in my lap leads to distraction.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

great responses so far, thanks! I learned that I was looking in the wrong area (behind the hinged panel that hides the jack, first-aid kit, etc.). I stupidly realized that I needed to remove the 2 nuts that appear on the trim panel closest to the hatch opening-they attach to bolts that are part of the taillight lens/bulb contraption.

Strangely, I had been unable to find photos of this procedure on the internet....unfortunately, I forgot to take any myself!