Dash board lights

[James Stern]

Just got my sl running after 4 years as a "garage queen".  All lights on the dash seem to be out.  I have checked the fuses and they seem all right.  I seem to remember the rheostat that controlled the dash lights was a little iffy.  Any ideas before I go pull the lights out one by one?

Jim

[Richard Madison]

Here's a first comment by a non-expert:

It is unlikely that all the bulbs are blown. Problem is probably some kind of "central" problem like the rheostat or an electrical  connection.

Annoying but to clean up the rheostat, the central instrument cluster has to come out. This is a bit of a job: the tach and speedo must be removed, the oil pressure tube has to be removed and capped; the temp gauge tube has to be removed (very sensitive to damage from bending). Should cap the temp cable engine port to prevent water from coming out.

There are specific instructions for removing the cluster in the Tech Manual or in other postings here.

While I had my cluster out, I sprayed the rheostat with Tuner Control Cleaner/Lube.

While the instruments are out it's a good idea to replace the bulbs since access is so difficult.

Also, it may be posssble to remove the rheostat knob and spray some cleaner throught the hole but this may fog up the glass...with a radio tuner it doesn't matter but you don't want a cloudy cluster glass.

Here's a photo of the cluster back and rheostat cover.

http://www.sl113.org/wiki/pmwiki.php?n=Electrical.Temperature

Richard M, NYC

[philmas]

Before pulling the whole thing out, just try and move the rheostat knob back and forth several times (but I assume you probably did that before posting!)until you eventually catch the "sweet spot".

It might be pretty sharp, and you sometimes won't get any light back,
but it's worth a try.

As for rheostat replacement, I was told it is NLA.
If yours is kaput, bypassing might be a better option.
I never felt the need for dimming the dash lights, as they're already dim enough even in the "full" position!

Philippe from Paris
'71 280SL manual 4sp

[James Stern]

Richard,

If you are a "non-expert" I wonder what that makes me?  The thought of removing the entire center cluster and taking a chance of messing up the temp gauge ( which does work) is pretty scary.  If I were to try the cleaner route what would you suggest?  It looks like the rheostat is held on by an allen set screw so should be easy to remove.  

Thank you for the prompt response.

Jim

[James Stern]

Phillipe,

You are absolutly right about the rheostat having a very narrow "on" spot.  As I recall before my sl became a garage queen the rheostat only worked in one spot and I have gone back and forth with the thing when I first found out the dash lights were not working. I agree that jumping the wire might be a solution but before I do that I thought I might try Richard's idea about a little bit of electrical cleaner.  Does anyone know how many seperate light bulbs were in the dash.  I read in one forum about replacing them with 4 watt bulbs as they are 2 watt bulbs according to the posting.

What a great car to drive in the "City of Lights".  You are so lucky.

Jim

[graphic66]

If you get the rheostat out, clean it up and put some dielectric grease on it to stop future electrolysis. I put the dielectric compound on all electrical connection, especially bulbs. It is a must have for these cars. You also may need to bend the little connector that slides along the spring just a little to get a better connection. Very light sandpaper can be used to clean the spring and the contact point of the tab that slides on the spring.

[James Stern]

Does anyone have an underdash wiring diagram for the 280sl?

Thx,

Jim

[Peter van Es]

quote:Originally posted by James Stern

Does anyone have an underdash wiring diagram for the 280sl?

Jim, if you're a full member you can find full colour wiring diagrams in the Technical Manual. If not, here's a black and white copy for the 280SL: http://www.sl113.org/wiki/pmwiki.php?n=Electrical.WiringDiagram

Peter

1970 280SL. Also known as 'admin@sl113.org' and organiser of the Technical Manual.

[James Stern]

Richard,

I would like to try the easy route.  How do you remove the rheostat knob.  Is there an allen set screw or do you just pull on it?

Jim

[Naj ✝︎]

quote:Originally posted by James Stern

Richard,

I would like to try the easy route.  How do you remove the rheostat knob.  Is there an allen set screw or do you just pull on it?

Jim

No, Don't try that. There is a circlip behind the glass holding it in place.

naj

68 280SL

[James Stern]

Naj,

Thanks for the reply. I have been cruising the forums about how others have resolved the issue and am trending towards removing the tach and bypassing the rheostat.  What is your opinion on that?

Jim

[Naj ✝︎]

quote:Originally posted by James Stern

Naj,

Thanks for the reply. I have been cruising the forums about how others have resolved the issue and am trending towards removing the tach and bypassing the rheostat.  What is your opinion on that?

Jim

Yes, treat it as a project.
Clean all glass inside and out and new instrument bulbs etc. You may be able to clean up the rheostat and get it to function again...
You dont want to visit here anytime soon!!

naj

[jeffc280sl]

Jim,

My rheostat spring was broken very near its end.  I was able to solder the end and it works well.  

Download Attachment: Rheostat.JPG
43.22 KB

[James Stern]

Naj,

We try to get back once a year as our god-children live between Bath and Bristol.  Thanks for all the info you have provided but something has come up that makes it look like I will have to sell the Merc.  If this changes I will be back to you.

Best Regards,

Jim

[James Stern]

Jeffc,

Thanks for the .jpg.  If I don't sell it (will know in a couple of weeks) I will take your and Naj's recommendation and first take it apart and try and clean it and if that doesn't work I will shoot it.

Jim