Why oh why does my tail light bulb keep burning out?
 

82' 300TD - the dawg-gone driver's side tail light bulb burns out about once a year - seems each fall... no, really.

I've cleaned and tightened the socket... even treated it and the fresh bulb with dielectric grease last year; but here I am again - the bulb is once again burned out.

Might the light housing be possessed or something?

I've driven this car almost 5 years - never changed the bulb in the right side... but the left side needs a new bulb yearly. And each year I've checked the old bulb with an ohm meter - and yes, the bulbs are burning out...:confused:

Ideas?

I had the same problem in my 85 300D. The problem for me is that water droplets would drip on the light. drops of water apparently, when cold, over time, put put on the bulb was enough to burn it out.

Re sealed the taillight and mended the hold in the plastic housing and all is well now.

Strange.. been noticing this same phenomenon on my two TD'S....except on each of them it is the right side tail light. Last time they were changed I noticed the plastic around the socket was a bit melted looking?

Thanks for the thoughts... and water getting in had crossed my mind, as I try to imagine what might be causing my friendly annual warning from a uniformed officer ;)

Now that I think about it, the right tail light has been replaced - the left is original. I'll look it over more closely for cracks :)

ARe you using the correct small glass bulb?

The tail lights in my wagon used to fill up with water. I once dumped over a cup of water out of one of them. Check the seal around the lens and also look for cracks in the lens. I bought some closed cell phone once to cut my own new gaskets. New ones are spendy$$. You might also check the plugs that behind the lenses. Make sure you're wires are all good and clean, and have tight connections.

Here's a slow motion experiment:

Move the bulb from the right side to the left side of the car, and put the new bulb into the right side.

See which bulb burns out next year, and report back to us.

If I held my foot on the brake(brake lights on) and my wife slammed the trunk down the cheep replacement bulb would burn out every time. The original, never a problem.

I'm glad to report discovering something new - to me, anyway. Did you guys know the housing cavity in the body has a drain?

Well, I didn't. But knowing how well designed these wonders are, I probed a dimple in the floor of the cavity with a wire, while reaching up from twixt the body and bumper from underneath. Low and behold, a rubber drain tube - plugged up with goodies, my fingers beheld. A dribble of water from a wet rag from the top, and rolling the rubber tube in between my fingers from underneath, and the goodies washed free of the drain.

Now, is this my problem solved? I guess I'll let you know in a year or two ;). I'll also mention that this time the bulb was not burned out, but rather the socket contacts had gathered enough corrosion/grime to keep the bulb unlit. I've cleaned and re-treated the contacts, and also treated the cleaned and dryed seal around the outer edge of the plastic housing with wet-type silicone lubricant (to aid in keeping water out of the body cavity).

The drain, at least on my 300TD, is toward the tailgate from the screw you'll see projecting up through the floor of the tail light cavity. Might be worth checking on your own TD.

:)

What bulbs are you guys installing? I am considering installing LED bulbs looking to make them a bit brighter. They are terribly dim.

Looks like (2x) 1156 ? Not sure the third bulb, or if the 1156 is accurate.

LED bulbs would be brighter, there is also the populate tail light mod where you add a socket to the housing.

LED bulbs will also defeat the cruise control system.

7506 is the proper bulb looks like
http://qa.sylvania.com/en-us/applications/automotive-lighting-systems/Pages/lrgallbulbs.aspx?year=1983&qual=&model=101&make=60

I tried these ones, had them on hand from another car... but they made the brake lights look almost pink. :confused:

The color temp was too high, and they were oddly focused as well... Maybe read the reviews and stay away from anything lauded by anyone with a honda in their signature...

And what is this 'cruise control' you speak of? I think I had a function-less lever labeled cruise control once... :rolleyes:

Here is another good place to buy LED lights:

https://www.superbrightleds.com/cat/led-vehicle-replacement-bulbs/vehicle/1985-mercedes%20benz-300td--/37-3304--/

https://www.superbrightleds.com/cat/led-vehicle-replacement-bulbs/vehicle/1985-mercedes+benz-300td--stop+light/37-3304--965327/


The cruise control system uses the brake lights circuit as a safety mechanism. When the brake lights are in the off state the cruise control amplifier senses a path to ground and allows normal operations.

When the brake lights are on two things occur, the ground connection of solenoid inside the actuator is broken, mechanically disabling the cruise. The 12V signal also enters the amplifier instructing it to turn off.

When an LED light is installed it removes this path to ground and disables the cruise system as the cruise system.

If you're interested in restoring your cruise control system, drop me an email. I've worked on almost 800 units, the oldest of which is still working. 80,000 miles and counting in my 91 300D.

Actually, my current ride doesn't have cruise control installed, though I did get it working on my last 300D (about 10 years back).

As for led lights, they looked great all over my mini cooper, but I've only tried two types in my 240D. Neither seemed right. Just personal preference though... most should look fine so long as they are omni directional.