6W Instrument Bulbs Installed! Let There Be Light!

[Rolf-Dieter ✝︎]

My odometer light bulb in my 280 SL 1969 is burned out. Has anyone changed it?

Is it a big deal? What bulb size do I need?

Thanks for your help fellows

[66andBlue]

Since the odometer does not have its own bulb I assume you mean the speedometer, correct?
Take a look here: http://www.sl113.org/wiki/Electrical/Speedo
In the photos you can see two round sockets (one goes through the bracket) for the bulb holders and info on the bulb.
Not a big deal, but a PITA - because to get access to the bulb holders you need to remove the tachometer and reach behind and around the center cluster instruments. Easiest to remove all three instruments. See also photos here: http://www.sl113.org/wiki/Electrical/RevCounter

[pj]

The tech manual says OSRAM # 3796, so I found this document:
www.osram.com.hk/osram_hk/EN/Local_Activities/English_Catalog/OSRAM_Automotive_lamps_2009_2010.pdf
and if you go immediately to page 27, you will find 3796 listed there. But what interests me is that # 3894, just 3 lines down, has the same voltage, same socket, same bulb dimensions . . . but it's a 3W bulb, not 2W.
What do you think? Would it work to brighten up the speedo and tacho a bit if we used a modern 3894 when replacing the bulbs in our instruments? I presume it would draw 250 milliAmps from the electrical system instead of 167 mA, but would that be a problem?

OSRAM's a big company with at least some incentive to care about their heritage, so more ideas might be out there somewhere.

[ABikePeddler]

Well, I just went for it. Tired of barely being able to read my instruments at night I made it my Labor Day project to replace all the 2W instrument bulbs with 6W replacements and WOW, what a difference!  While the orangeish glow of the dim bulbs is somehow more "classic "Benz", being able to now see (and control) the dash lighting is VASTLY more practical.  Here, look for yourselves...

The before photo is actually just with the new bulbs turned down to approximately their old maximum dim setting using the rheostat.  The brighter images are at full brightness.  In reality they are not quite as bright as it appears on camera but they are vibrant, fresh and look "new".  I just love it.  Hoping the jump up from 2W to 6W won't lead to any issues.  We'll see.

 

[pj]

Hello Eric,
great idea! I think your first picture answers one of my long-standing questions because the upper half of my centre instruments is dark. I figure there are 2 bulbs in there and one of mine is kaput.
So how many bulbs did you need, and where did you buy the 6W bulbs?
But most important: how did you do it? Part of a bigger project to remove the dash? Or what?

[Cees Klumper]

As far as I know I have original 2W bulbs and I can see the instruments just fine. That is with the rheostat bypassed, so full strength. The only issue I would worry about with going to the 6w is the additional heat they might give off, and whether the wiring won't overheat (we don't want that!), but that may be a lesser risk.

[ABikePeddler]

Heat. That is my concern also... additional heat as well as the additional draw on the cars 48 year old wiring. But I ran these new 6W bulbs in the tachometer since April with no ill effects.  (I didn't finish installing the remaining bulbs until just this weekend.)  Below is a picture from April showing the new bulbs in the tach while the old bulbs remained in the rest of the instruments....

I purchased the bulbs from Candlepower.com here: http://store.candlepower.com/38xefiinpala.html   You will need 5 bulbs total to replace the existing bulbs in the 3 main gauges.  I purchased extras in case I had any D.O.A bulbs from the retailer.

Note: As with even the standard bulbs, the speedometer is slightly less well lit then the tachometer.  That is by design.  It's just the way the bulbs are situated behind the gauge face that causes this uneven lighting.  Not much can be done about it. 

As to the question about the center gauge having two bulbs, mine only had one which is located direct center in the rectangular gauge cluster. Because the bulb is located in between the 4 small gauges I decided the best way to access it was the pull out the oil pressure gauge (which is held on with two small screws on the back side of the gauge) so I could gain access to the bulb.  It is a tight fit trying to remove that bulb with bare fingers but it worked fine and the new bulb slotted in with ease. The center gauge does have other bulbs (turn signal, low fuel light etc...) but they are not related to the main objective of overall gauge lighting. Once installed, I recommend carefully wiping down the bulb glass if you have to handle them with bare fingers.  Right or wrong, I have always heard that the oils from ones skin can cause a shorter life for the bulbs.

There are numerous excellent write-ups on this forum about how to remove the gauges so do some searching.  Most all of them comment on how difficult it is to remove the gauges from the dash. I did not find this to be true at all. Sure, it is a tight fit reaching up behind the dash to first undo the tachometer but from there, it really isn't a big deal.  Whole project was done in less then 2 hours and that was including removing the chrome bezels so I could clean the glass and inside of gauges. 

Next:  Remove the HIVAC (Heating Ventilation Controls) controls and install new bulbs in there.  My controls work fine but the current, original 2w bulbs barely qualify as lighting and the Lucite controls themselves are so filthy they are not illuminating as they should. Will try and post pics of that project when I can.

[66andBlue]

Bike Peddler,
for how long did you run the bulbs continuously at full power, 10 minutes, 1 hour, 5 hours?
I would be worried about putting 12 watt heat into small space like a speedometer -  my circuit board soldering iron produces 12W !!
Like you i wanted brighter lights but decided to exchange them for 4-LED bulbs since they stay cool:
https://www.superbrightleds.com/moreinfo/ba9s-ba7s/ba9s-led-bulb-4-led/6/
The photo shows the effect of the rheostat.
I'll put more info on LED changes into the technical manual soon.
 

[Rolf-Dieter ✝︎]

I like to add my 2 cents here ... In real life Engineers and Designers use components that are safe and right for the application. That also applies to our cars. If you change things you take the risk of asking for trouble. I have to change a bulb in my speedometer, however, the bulb that came out will be replaced with a new one of the same make and wattage.

Be safe fellows ... don't take risks replacing wiring can be a major project, if it turns into a fire you may as well kiss your Pagoda good bye.

Peter, changing bulbs on our cars is not the easiest task. I'll show you next time you come by my old odometer how to remove the mounting bracket, then the protective cover to gain access to the bulbs and finally using two finger tips pushing in the bayonet-type mounting bulb to remove it. All this after one removed the tach.

There is a write up in the Technical Manual as to how to remove the tach.

Link right here ---> http://www.sl113.org/wiki/Electrical/Speedo#Lights

[ABikePeddler]

66andBlue: I have been running the bulbs in the tachometer since late April.  I drive the car daily, much of the time with the lights on, so I'd estimate I have over 25 total hours run time on the 6W bulbs in the tachometer with no ill effects.  But I didn't expect there to be an issue with these bulbs until I installed the remaining 3 bulbs as the real draw on the system would only happen once all were installed.  I will update this post if there is ever an issue. 

Your LED lighting looks fantastic!  As with most LED's, the lighting is usually a little blue.  Is that the case with yours?  (Hard to tell from pictures) Also, LED's generally are not dimable... is that also the case with yours?  I like the idea of using LED's as there really isn't many drawbacks to them... low cost, low energy usage, low heat, and super long bulb life.  Negatives usually are unnatural color lighting and lack of dimability.   

[66andBlue]

Peddler,
I do not perceive them as "blueish" but cool white, certainly not warm as the incandescent, and yes they can be dimmed using the rheostat in our cars. See my photo, the upper photo shows the lights dimmed with the rheostat.
But not all bulbs in the center cluster instrument can accept LED.  More on this in the technical manual later.

Rolf-Dieter,
I agree that one should not "... take risks  replacing wiring can be a major project") but please notice there are no wiring changes.
The 4-LED bulb draws less than 30 milliAmps compared to 0.14 Amp for a 2 W bulb (at 14V)  or 3x more for the 6 W bulb. So they are safer and more economical and I bet the MB engineers would have used them too 50 years ago.

[garymand]

I've wondered why the lights are so dim with with the pot full on.  2w is not much light from these filiment bulbs.  Maybe the Germans thought it would be best for night vision to use very low wattage AND further reduce the intensity through the pot.  To put some fears aside: 1) oil on the bulbs has no effect on filliment life, it is outside the glass.  The filliments are in a vacuum and unaffected by paint or oil to any measurable effect on the outside. (the bulbs that have that warning are very high intensity projection bulbs and I'm not sure I understand the problem issue other than the glass cracking. 2) apparently the pot never gives full current to the bulbs as Cees says they burn brighter with it bypassed.  So they aren't getting the full 5-6 W.  Thanks Cees, I've wondered about why the bulbs never go to full bright white light.  4) Heat?  well the wiring is more than ample for the current, the wires won't heat up, but the heat from the bulbs might be a problem if they are surounded by plastic that may be heat sensitive.  5) You can turn the brightness down to some comfortable level. 6) I and I'm sure many of you have replaced dash lights in other cars, 5W is about normal for what I see in other cars.

But ,,,I really like the led version especially if we can dim them.  This isn't something I would do on a whim, but I need to replace my ignition switch and speedo cable anyway.

BTW, Nice result pictures, thanks.

[66andBlue]

...  To put some fears aside: 1) oil on the bulbs has no effect on filliment life, it is outside the glass.  The filliments are in a vacuum and unaffected by paint or oil to any measurable effect on the outside. (the bulbs that have that warning are very high intensity projection bulbs and I'm not sure I understand the problem issue other than the glass cracking.

See: http://en.wikipedia.org/wiki/Halogen_lamp
Any surface contamination, notably the oil from human fingertips, can damage the quartz envelope when it is heated. Contaminants will create a hot spot on the bulb surface when the lamp is turned on. This extreme, localized heat causes the quartz to change from its vitreous form into a weaker, crystalline form that leaks gas. This weakening may also cause the bulb to form a bubble, weakening it and leading to its explosion.[18] Consequently, manufacturers recommend that quartz lamps should be handled without touching the clear quartz, either by using a clean paper towel or carefully holding the porcelain base. If the quartz is contaminated in any way, it must be thoroughly cleaned with alcohol and dried before use.

 

2) apparently the pot never gives full current to the bulbs as Cees says they burn brighter with it bypassed.  So they aren't getting the full 5-6 W.  Thanks Cees, I've wondered about why the bulbs never go to full bright white light.  

I don't think Cees wrote what you think he did.  
In any case it is not correct. A well functioning rheostat will change the resistance from 0 Ohm to to 18 Ohm and there should be no drop in voltage caused by the rheostat. If it does then it needs to be cleaned!
See: http://www.sl113.org/wiki/Electrical/Rheostat
Incandescent light bulbs do turn dark slowly with age and thus become less bright. No need to blame this on the rheostat.  

[ghenne]

Surface contamination is indeed a problem with halogen bulbs, because of the heat they output. However, are these bulbs halogens?

[Sableco]

Hello 66andBlue
I would agree that the Led lights are a better choice for the advantages mentioned by all.
the vendor offers them in 32 or 90 degree light bulbs, which ones did you use?
Thanks a lot for all the info.

Basem

[pj]

Hi Alfred,
those LED bulbs from the superbright website look very interesting and quite reasonably priced. Did you buy the "Cool White" colour? Any thoughts on what the other colours would look like in our instruments?

[garymand]

Ahh yes, Halogen and vitrious quartz envelopes, bubbles form and the envelopes explode.  I understand exactly what that says.  I'm glad I can still handle ordinary light bulbs with my bare hands.  I'd hate to have the bulbs in my house, or dash board, blowing up around me. 

[garymand]

Take a look at this parallel topic,  basically no problem with 3W some are using 6W and not mentioning and blown fuses.  If you count all the bulbs on the circuit and multiply by .25Amp (250mA), the answer should be 1/2 the fuse Amp rating.  If there are 8 bulbs X .25 = 2 Amp.  With 8, 6W bulbs its still just 4 Amps.  Or you might want to go to LEDs as covered in the topic. 

[Rolf-Dieter ✝︎]

Thanks Alfred, Yes I did mean the Speedometer. I explored the issue a few days ago by disassembling the old one I got with the car having the original milage. I also found the write up in the Technical Manual. I will (once I get a set of replacement bulbs) remove the speedometer and change out the bulbs. There is no urgency since I don't intend to do much night driving perhaps on my way home from Williamsburg, VA I may put in some evening driving.

Meanwhile I'm following the thread of "6W Instrument Bulbs Installed! Let There Be Light!" Perhaps I will change them all out to a bit stronger Wattage.

[49er]

Sorry guys but I still like the old timey look of the original "dim" bulbs. Maybe when and if the day comes when I need to replace them,  I might change my mind.

John

[garymand]

We get used to them, don't we.  I really do think they are dim on purpose for better night vision.

[66andBlue]

John and garymand,
I agree with both of you. I also prefer to have dim lights at night time (in any car I drive) and for this reason I would never bypass the rheostat. It is during twilight that I want brighter lights and the LED are almost perfect for this.
When you took this photo, John, were the lights at full brightness?

[66andBlue]

Hi Alfred,
those LED bulbs from the superbright website look very interesting and quite reasonably priced. Did you buy the "Cool White" colour? Any thoughts on what the other colours would look like in our instruments?

Peter,
unfortunately at this time the Ba9s 4-LED bulbs are only available in "cool white" (plus blue, green, yellow and red) but my guess is that in the near future there will be "warm white" available also. The company already sells a Festoon bulb in "warm white".

...the vendor offers them in 32 or 90 degree light bulbs, which ones did you use?

Basem
for the tachometer and speedometer and also for the center instrument panel I used 90 degree 4-LED.
All the other bulbs in this cluster are 1-LED and also 90 degree. 
Note that not all bulbs can be replaced with LED!
The red indicator light for battery charging (which is also the warning light for "door open" and "low brake fluid") must have some resistance otherwise the charging circuit is compromised!
The opening for "low fuel level" warning light in the housing (on the left in the photo) is too narrow to accept a 1-LED.

[garymand]

Nice pic, I better get my order in before they run out of stock.

[garymand]

Does the stock flasher work with the LEDs or do we also need the LED compatible electronic flasher?