Hi guys:

I recently picked up a 96 E300D with 167K and am in the process of sorting through the problems. I could use a few suggestions on an electrical issue at the right rear stop light.

It's out.

The left rear stop light works. And when I swap the stop lamps left for right, the problem stays on the right side. The previously not working right lamp happily lights off when it's placed in the left lens assembly. So the bulb is not the culprit. Neither is that little plastic holder that the holds the bulb. What is next?

Is this merely a bad contact in the right lens assembly or something more sinister in the wiring?

My next thought was to clean the contacts on the right lens assembly, but I've got to tell you, the entire assembly along with the lamps could pass for new. Also I didn't see much metal to clean, but I haven't dug into it yet.

Thanks in advance. Also thanks to the list on another problem, the left rear window regulator. Using write ups and photos from this list, I replaced the regulator in record time. Took me about 15 minutes to successfully remove the door panel and regulator, and another 10 to get the new regulator pop riveted back in.

While I'm at it, here's another problem. The engine knocks like a rod is busting out. Then the noise goes away. This occured after sitting in a long line of traffic on my way to work yesterday. Engine starts and runs smooth as silk, compared to my W123 wagon. All of a sudden, knock, knock, knock at idle and higher RPM. Sounds like a single cylinder is knocking. I pull over and wait 30 seconds for the rod to come out of the engine. It doesn't.

I get into a parking lot and raise the hood, the knock sounds like it's coming out of the intake side, and not down lower on the block. So it's not a rod. To my great suprise the knock recedes and then quits altogether. Again runs smooth for another 100 miles. This is my first experience with this engine, I'm used to the 4 and 5 cyl. diesels in the older W123's.

Since acquistion, the car has been successfully driven about 400 miles. Before that, it's probably sat for quite a while. I've filled it up once. It came with 1/2 tank of fuel, age and condition unknown.

Thanks in advance,

Ed

Once you've used a meter to determine that your left-rear light socket does or does not have voltage and you are sure that all of your fuses are good I'd check out the bulb failure warning relay.

There is a specific name for it but I can't remember it. In the 123/24/26 series the unit will light a bulb on the dash telling you that a light is burned out. I believe in your car (I think you are a w210 - but I'm not positive and you don't say) there may a string of text that gives you specific information when a dash 'warning light' is illuminated.

If your car does have the more complex dash information system then I am not certain where or exactly how your bulb warning relay functions. In my car (w124) when I had the same problem as you I needed to replace the relay.

On my 97 E300 I had problems with intermittent brake lamps. Found that even though the plastic bulb holder seems tight, cleaning the contacts and "refreshing" them to ensure good contact made the difference.

The knocking...without knowing more and the car being new to you, I would guess water or other contamination in the fuel.

__________________
Mark in MA
05 MB E320CDI 402k Granite Grey Metallic
05 MB E320CDI 267k Black
05 MB E320CDI 232k White
05 MB E320CDI 209k Tectite Grey
99 Dodge 2500 Cummins 5sp 148k
62 Jeep CJ-6 120k

I learned about this the hard way on our E320 97.
Every time that the rear light went out I ended up buying a new tail light assembly, the reason is CHEAP construction.

What happens, every time a new light bulb is forced and turned into the socket the pressure destroys the cheap contacts around the socket that sends signal to the computer, once that happens all you can do is to replace the entire assembly for yet another one.

Vahe

I'd try a new bulb holder first.

The knocking may be an inj with a bad spray pattern or dribble at idle. Basically causes a miss fire. Sounds like someone is trying to beat their way from inside out using a 3lb hammer. Is impressive.

__________________
Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

I recently had the same problem. I found that by not twisting the holder in all the way that I was able to make sufficient contact keep the light working. It's only been a month and about 4k miles, but I'm hoping it's enough.

I fixed this problem over the weekend. I didn't take photo's, but here is a verbal that might help someone. The good news is that is does not cost a cent to repair.

The symptom:

Brake light is out, but the bulb tests good. Dashboard display shows lamp defective alarm.

The problem:

Poor or no contact between lamp holder tab and lense assembly plate.

The cause:

Brake lights are brightest, they draw more current that the other lights. They can be on longer if the operator rides the brakes. This mismatch between DC current requirement and surface area of contacts tabs combined with weak holding force causes hot spots on the contact surfaces. Heat spreads to plastic support structure, softening the plastic and melting the backing plate into the plastic substrate. This causes arcing, pitting and additional heat until electrical connection is lost. Plastic then cools and rehardens into a sunken, non-conductive position. Lens assembly is replaced with same design, and the cycle begins again.

Technical Commentary:

There is not enough surface area for the material being used on the contact surfaces between the lamp holder contacts and the lense assembly contacts. If the material were copper, it might work, but it's some kind of tin, I don't really know the exact composition. Anyway, it's not a good enough conductor to pass that much current over that much surface area. That's why it keeps happening to those of you who replace your lense assemblies. A few possible solutions present themselves:

1. Reduce the current draw of the brake light.
2. Change contact material to a higher conductivity metal-like copper/silver/gold.
3. Increase surface area of contact points.
4. Increase holding force of contact points.

I did #3 and #4 because it was cheap(free) and easy, and fast. Plus I couldn't find my soldering iron. I was going to add material to the contact points, but this will work for now. But the problem could also be solved by switching to lower current draw brake lights, say LED's. You could also fix the problem by somehow adding a copper tab to the contact surfaces, but that's impractical in the general sense, unless you have a little copper tab sitting in your parts bin.

Remove the lens assembly from the car:

Unplug the electrical at the connector: Squeeze the sides and pull straight down.

With an 8 mm socket and extension, remove 4 nuts holding assembly to vehicle. Push, wiggle, shove the assembly off the car. It will take some force as mine was stuck to the rubber gasket and I had to push hard. Remove assembly to bench or kitchen table.


Remove the bulb from the assembly:

Twist the bulb holder counter clockwise, remove bulb holder and observe the contact point on both the bulb holder and the corresponding lense assembly.

Clean the contact area:

Using any available abrasive, sandpaper, emory cloth, butter knife, remove carbon down to shiny bare metal on both the bulb holder tang and the lense assembly plate. When I did this, my contact plate was pitted, indicating high current densities. By grinding the area flat, I also increased the space between the contact points, which we have to correct.

Modify connectors to increase contact pressure:

Bend the tang on the bulb holder out so it sticks out farther than it did before.

With pliers, bend the flat plate of the lense assembly up until it makes contact with the tang. This will take repeated bending and test fitting until you get a solid contact. Since the lense assembly metal is made from some tin-like material, it's rather hard to bend on a micro scale. I bent mine to an acceptable position in two bends, but you might take longer. There is also the matter of the plastic support substrate that's been melted and made brittle. As I bent mine, I broke the plastic support tabs, but realized that it didn't matter because the metal plate is supported by a lot of plastic tabs. Breaking one or two didn't matter, but one could always epoxy them back in if necessary. The idea is to bring the two mating surfaces back into contact.

Test for satisfactory fit:

Visually inspect the contact area whilst fitting and un-fitting the bulb holder. You can see that the fully seated position puts the contacts and the bitter end of the backing plate. That's where all the damage occurs and why inserting the bulb in part way also fixes the problem. It moves the contact point of the bulb holder to a fresh bit of backing plate.

Reassemble the light:

Reverse of disassembly.

Test:

If you took your time and saw where the problem was, this part is a non-event. Others will need to verify that their changes worked to make the contacts conduct again.

Longevity:

Maybe another year or two. This doesn't fix the root cause of the problem, but it does get the light back in service for zero dollars. Plus the next time it will be easier to fix, you already know what is wrong.

Regards,

Good on ya for fixing the light. On your knock, I'd suggest driving the snot out of it for a tankful. My '95 has 341K on it, original injectors, original timing chain, and at least once a week I floor it up through about 80 mph. Shifts right about 5000 rpm - if less than that I know it's time to change the fuel filter.

Rgds,
Chris W.

__________________
Objects in closer are mirror than they appear.

Chris,

You'll appreciate this. The other day I entered the on-ramp to the local interstate and floored it. It ran up to 5K + RPM before it shifted. I even think I saw the needle hit the 6K number for a moment.

A big clould of black smoke shot out the back. Drove home and shut it off. The next morning when I started it again, all the codes were cleared from the alarm panel. No more injector alarm, no more mass air sensor alarm. It's been alarm free for three days, and it still runs fine. That and the tail light fix has cleared the alarms. Now on to the cosmetics.

I'll do a diesel purge in a few weeks if the alarms return.

Ed