Author Topic: instrument lights blowing fuse  (Read 2739 times)

piddler

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instrument lights blowing fuse
« on: December 01, 2018, 18:04:10 »
I have a '67 230SL and am blowing #7 fuse. I think I have chased the problem to the instrument lights. When I turn the rheostat that controls the brightness of the lights, the fuse blows. My problem is that I don't know how to get to the rheostat or lights to check them.

I don't have a maintenance manual. Mine was lost during some of my moves.

Thanks for any help, Pete

piddler

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Re: instrument lights blowing fuse
« Reply #1 on: December 01, 2018, 19:59:30 »
I had more time to do some checking. I have the handshake connector disconnected and when I checked the rheostat according to the instructions in the technical section there was no continuity from then pins indicated. That tells me that the rheostat is bad.
I disconnected the right front and rear lighting connections and with the handshake connector disconnected the fuse would still blow when I turned the rheostat.

Out of time to work on it anymore today. Will get back to it next week. Any advice or suggestion are appreciated.

Thanks, Pete

Pawel66

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Re: instrument lights blowing fuse
« Reply #2 on: December 01, 2018, 20:46:36 »
with the handshake connector disconnected the fuse would still blow when I turned the rheostat.


I thought this connector connects everything in instrument cluster... ??? ???

Are you sure you disconnected the correct handshake connector? Sorry for a silly question...

« Last Edit: December 01, 2018, 21:03:11 by Pawel66 »
Pawel

280SL 1970 automatic 180G Silver
W128 220SE
W121 190SL
G-class

114015

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Re: instrument lights blowing fuse
« Reply #3 on: December 01, 2018, 23:20:17 »


Hello Pete!

Do your instruments lights work at all? Do they work if you disconnect and jump the rheostat?

To me it appears as if you have a shortcut because either the rheostat itself or one of the terminals of the grey-blue wires behind the instruments touch ground - which they shoudn't.
Unfortunately the instruments bulbs are held with brass bulb holders to which the grey-blue wire is connected with a little screw in each case - and there are four of them (2 each for the speedo and the rev counter). Those "ends" are exposed o the elements (i.e. without further insulation) und thus just prone to come into contact with ground if you do not assemble your instruments with care. - Just a bad design.

Please check this and also whether your rheosotat touches ground - which it shoudn't.

Good luck !

Achim



Achim
(Germany)

piddler

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Re: instrument lights blowing fuse
« Reply #4 on: December 02, 2018, 00:31:22 »
Thanks for the responses.

I am pretty sure I have the right connector disconnected. It is the one directly below the steering wheel. I,too, thought that it would disconnect all of the insturment cluster.

I will get back to it next week.

Thanks, Pete

66andBlue

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Re: instrument lights blowing fuse
« Reply #5 on: December 02, 2018, 19:41:46 »
There are two handshake connectors, one for the center cluster and the other for the column multifunction switch. When in doubt disconnect both. 🤔
https://www.sl113.org/wiki/Electrical/Rheostat

Also check whether a PO already tried to shorten the rheostat and some solder remnants cause the short.
« Last Edit: December 02, 2018, 19:54:15 by 66andBlue »
Alfred
1964 230SL manual 4-speed 568H signal red
1966 230SL automatic 334G light blue (sold)
1968 280SL automatic (now 904G midnight blue)

piddler

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Re: instrument lights blowing fuse
« Reply #6 on: December 02, 2018, 22:44:17 »
I disconnected the other connector and sure enough, the first one was the wrong one.

 I now have the rheostat to where I can work on it. Since I don't know if the problem is with the rheostat or the lighting I am going to melt the solder on the rheostat  and remove the wires and short them. If the short is still there then I will look further.

Thanks, Pete

66andBlue

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Re: instrument lights blowing fuse
« Reply #7 on: December 02, 2018, 22:58:07 »
Those connectors can fool you - that is why I labeled the in and out cables on one red and on the other blue as you can see in the tech manual.
Alfred
1964 230SL manual 4-speed 568H signal red
1966 230SL automatic 334G light blue (sold)
1968 280SL automatic (now 904G midnight blue)

piddler

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Re: instrument lights blowing fuse
« Reply #8 on: December 03, 2018, 13:20:10 »
Good idea.

piddler

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Re: instrument lights blowing fuse
« Reply #9 on: December 03, 2018, 23:19:39 »
I think I found the problem. The insulator on the bulb holder was missing on the tach.  I hope that was the problem. I had forgotten what a pain it is to get to the instrument lights.