Bulbs frequently out
 

I've never owned a car that has had so many light bulb problems. The
"bulb out" light on the dash comes on at least once a month it seems.

Though I've replaced the headlamps and some others, it's usually the right rear corner bulb. I've replaced it probably 4 times in the last 2 years. Last night, it was the left brake light (not the one when you actually brake, but the one that lights up when the headlights are on). That light has never been a problem in the 2 1/2 years I've owned this car. When I barely touched the bulb, it started working again, and all is well.

What is up with this? I don't like driving cars with warning lights on all the time. I doubt the fuse could be in question, but I'll check it. I'd probably put new fuses in 2 years ago anyways.

Thanks.

jeff 1991 300d, 128k

The only thing I can think of that would cause bulbs to fail in the manner you describe is too-high system voltage due to (perhaps) a faulty regulator in the alternator. It might be worth connecting a voltmeter to the car so you can watch it (carefully) while you drive. System voltage should not get over 14 volts.

The bulb that started working when you touched it could be a victim of corrosion; do you live in a humid part of the world? There could also be a tiny water leak into the tail light. Check and clean (polish with fine steel wool) the bulb and socket; protect future bulbs with a very light coat of dielectric grease (use Vaseline if you don't have dielestric grease). Use very little and wipe off most of that, then put the bulb back in its socket.

Jeremy

I have the same problem in my car. Fiddling with the bulb gets it working again. It's been the right brake bulb on a couple of occassions but the rear corners are the big headache. I can clear the warning light by pounding the left corner lens from outside. The right one is infuriating. With the bulb holder assembly in hand, I can move it any which way, shake it, pound on it, and the bulb will stay lit. Once I put the holder into the lens housing, the bulb goes out. Argh!

What I've yet to try is bending the receptacle tangs so they grip the bulb more tightly. I didn't think of dielectric grease. I should try that.

Jeremy, the bulb and tail light contacts look new.

Sixto
87 300D

I have the same problem. I really like how easy it is to change bulbs in the Mercedes though, keep spares in glove box. I took both bulb holders out after replacing a bulb here and there, lot of the bulbs were corroded and broke off when I tried to remove them, after getting the bases out I did as suggested cleaned sockets, light bit of dielectric grease on bulbs and reassembled, still had dash light come on and couldn't find a burnt out bulb so I just drove that way, connections must have been made because dash light went out, don't think its burnt out because it comes on with others when I start car. Should replace tailight lenses as they are a bit fadded and one side has minute cracks, wish I could find new ones for less than I've found them so far. Replaced front headlight covers really make a difference looks wise.

driver's side reverse light
 

Coda suffers from this same thing, but with a "twist".

I changed the driver's side reverse light and then a week later, I notice the bulb out indicator was lit; sure enough the driver's side reverse light is out. Of course, the indicator only comes on when in reverse.

But the real twist......is the poor ground in Coda's instrument cluster. Either the fuel gauge is NOT dancing around or the bulb out indicator is properly functioning ---- both things do not work at the same time. UGH.

I've come to the point where I've given up on "slapping the dash" to get the fuel gauge to work correctly and instead, just put my reading glasses on to read the trip odometer.:cool:

Bulbs are very simple to change and cost next to nothing; I have noticed that Mercedes seem to eat them as well.

Stop concentrating on the bulbs and fix your grounding system...

My SDL eats the left rear marker light. I replaced it twice and it just went again. I am going to remove the socket and really clean it this time. The BMW would light up the warning for the brake lights constantly (even when they were working) it was corrosion in the socket that was causing this. A few minutes with 00 steel wool solved that problem.

My SDL used to eat rear brake lights. Than I got frustrated and replaced them all with tinned Anchor's I got from the marina. That was two years ago and knock on wood they are holding up.

I think the boat bulbs are better than the auto ones.

These are fascinating problems; I wish I could come up with an intelligent suggestion but you all seem to be already doing the same things I would do.

You don't need to since I have already posted it...
what these lights have in common is the ground...
what burns our lights is not typically over voltage... but excess current due to too high a resistance.... due to bad grounding....

Okay I'll buy the grounding idea, I've done the battery and a couple of others. Anybody have a diagram showing where they are?

Negative battery to engine
Engine to body
Negative battery to body
?
I do not suggest vaseline anywhere near any electrical connector.
My father put it on the battery posts once to try to keep corrosion from forming... it did that well ... but insulated the post from the battery cable...

I = v/r
 

The Physics Police will arrest you for that one! A bad ground (or anything resistive in series with a load) will reduce the current through the load, not increase it. Bad grounds do not cause bulbs to burn out unless there is some other mechanism at work. I = V/R!

Corrosion where the bulb contacts the socket will gradually worsen due to environmental effects (primarily moisture) plus heat from the bulb as well as heat generated in the corrosion (which acts as a resistor). The corrosion gradually insulates the bulb from the socket until the bulb can no longer get enough current to run, but the bulb does not burn out.

Jeremy

Thanks, I thought there might be more than that, did do them, will recheck to make sure they didn't loosen up. I thought the vasoline on battery terminals was to cover them after the terminals and battery had been cleaned and then reattached, I use dielectric grease, is it better?