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Old 06-01-2007, 11:13 AM
Sapperbmet's Avatar
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Location: Manteca, CA
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1982 300SD interior lighting

I recently acquired a 1982 300SD with many issues, most of teh issues I have been able to address without asking for help, this one's got me confused though. I have no instrument/dash lights. I have determined that there is a fiberoptic system that deliveres light to the dash switches.

I have, however failed to locate the source of the light. All fuses are in operating condition.
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Old 06-01-2007, 06:32 PM
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Whats next?
Join Date: Sep 2005
Location: Coolum Beach, QLD, AUS
Posts: 284
First thing to check is the dimmer switch, it is the knob which resets the trip odometer and often inadvertently gets turned down. Try turning that and see if that works.

If not, it may be the dimmer rheostat, they commonly go west in cars this age. You will need to pull the instrument cluster to get at this, do a search it has been written up many times.

If it is the globe which feeds the fiber optic - and the fiber optic only lights a handful of switches in the center dash, it is located down behind the ashtray. Remove the ashtray insert, undo the 2 Phillips head screws holding in the ashtray frame and remove and peer down forward, you will see an 'octopus' of fiber optic wires (usually 6) coming out of a unit with a globe in the middle. You need small fingers to replace it - but it is easily done.

However, if ALL your instrument and switch lights are out - and you say the fuses are fine - my bet is either the dimmer knob turned down or a faulty dimmer rheostat.

Hope that helps.
1988 W126 420 SE

beware of fundamentalists!
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Old 06-01-2007, 11:04 PM
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Join Date: Jan 2007
Location: Manteca, CA
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It sounds like it will be the rheostat. I've checked and rechecked the fuses and the dimmer know, hoping against hope that it was an easy fix.

I also did locate the fiberoptic globe, although, on this car it is located behind the switch cluster, for me to access it, I had to pull the ashtray, radio, switch cluster plate and finaly the enviromental controls, as I do not have the smallest hands in the world. End of the day, the globe and bulb appear to be working correctly, they just do not have any power going to them.

Of course as I will be parking my 500SEL until I can put more emissions controls on it, I might steal the rheostat from that one.

1981 500SEL 182,000 kilometers
1982 300SD 262,000 miles
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Old 06-03-2007, 01:37 PM
Sapperbmet's Avatar
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Join Date: Jan 2007
Location: Manteca, CA
Posts: 36

Sure enough it was the rheostat on the rear of the dimmer post. As a temorary fix I soldered a jumper across the back of the rheostat, instant fix.

I do not, however, advise doing this on the side of the road, at night; after you run a diesel out of fuel beacause the fuel gauge was not 100% accurate....

Lesson learned

1981 500SEL 182,000 kilometers
1982 300SD 267,000 miles
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