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Old 03-31-2008, 08:51 PM
Registered User
Join Date: Apr 2003
Location: SoCal
Posts: 134
123 and 126 dash lights problems


Can someone lead me to or send me pics of the results of using higher than normal light bulbs in the earlier (early to late 80's 123's and 126's)? I understand it melts or burns the plastic optics.


1960 190D (college car), gone
1995 E300D, 290 k
2004 Infiniti G35 (spouse mobile)
2003 Nissan Frontier Crew Cab
2007 Jeep Grand Cherokee Overland 3.0L MB diesel
1978 GMC Classic Motor Home
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Old 03-31-2008, 09:58 PM
Registered User
Join Date: Nov 2007
Location: Snohomish, Washington
Posts: 47
Melting instrument cluster parts

My experience has been that the PO had 5W instrument cluster general illumination bulbs where there should have been 3W (194 style bulbs). The result was seriously melted and deformed prisms adjacent to the bulbs and some melting/warping of the white plastic that surrounds the bulb. The latter is often evidenced by light leaking over to the turn signal light area so that they appear partially on all the time.

My solution was to find a good used instrument cluster with good prisms and good white plastic surrounds (eBay) and then stay away from 5W bulbs.

I have since done some experimenting with lower wattage LEDs, with mixed results. One attempt seemed promising, but the illumination angle of 35 degrees was not adequate to reach the prism, which is not straight ahead of the bulb (I think it is higher). This attempt using LEDs from (30 mA at 12V, so very low wattage)

Another attempt was with an SMT surround light LED from These put out 1.5W, which is a lot for an LED in this usage. Unfortunately, I tried these not knowing that my prisms were already melted. When I get around to it, I'm going to try again with the new cluster shell and prisms.

General conclusion to date: the prism and light tunnel design sucks and there is not a whole lot you can do about it.
1981 300D 202K daily driver
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Old 04-01-2008, 10:27 AM
83 300SD
Join Date: Mar 2007
Location: Shawano, WI
Posts: 691
I have used the LED lights in both my 240D and 300SD with good results. After cleaning the prisms with alcohol/windex, I lined the cavity that surrounds the bulbs with reflective aluminum tape. Verify that the tape does not contact the circuit wiring. Much brighter than stock.

Certified Registered Nurse Anesthetist (CRNA)
2002 F250 powerstroke with Plantdrive WVO conversion
1983 300SD 190K miles ,sold
2006 E320 CDI
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Old 05-31-2008, 02:36 AM
Registered User
Join Date: Feb 2008
Location: DFW area (north side)
Posts: 1,288
frosted bulbs in dash

I've been replacing the original burned out baseless bulbs (3W?) in my 123 CCU. I think they are the original ones and I have some minor issues with melting near the bulbs. The bulb behind the headlight switch looks the same but is frosted (no melting). I can not find any markings on the bulbs. Are the frosted ones lower wattage?
Where can you buy the frosted type? I'd rather have dim lights if it avoids the melting.
1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale:
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Old 05-31-2008, 09:41 AM
daw_two's Avatar
diesel enthusiast
Join Date: Jan 2007
Location: Germantown, TN
Posts: 5,438
Melted Plastic

I don't know if I still have the pics, but "Elegant Madame" had melted plastic and browned light tunnels. The picture below is from a parts car. Any questions?
Attached Thumbnails
123 and 126 dash lights problems-dscf1809.jpg   123 and 126 dash lights problems-dscf1808.jpg   123 and 126 dash lights problems-dscf1810.jpg  
Germantown, TN

Current Car --- 05/2012 1984 300D Light Ivory, Red interior
Cluster Needles Paint
New Old Stock (NOS) parts

3/2008 1986 300SDL "Coda"
04/2010 1965 190D(c) "Ben"
& many more
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Old 05-31-2008, 10:00 AM
Chad300tdt's Avatar
Benzless Scoutmaster
Join Date: May 2007
Location: North Wales, PA
Posts: 4,001
Check this thread for links to the LEDs needed:
LED replacements for light bulbs?

I am very happy with the results, but my prisms are clean and in good condition and I used the silver tape as well. BTW, I put all new, stock wattage incandescent bulbs in my CCU and they melted the socket for the temp wheel. I am now replacing those with the 74 Wedge Base LEDs to keep any more melting from happening.

On a side note: After replacing my dome lights with LEDs, I accidentally left the front dome light on overnight. The next morning the battery was fine and didn't need a jump or charge. Another benefit to using low power consuming LEDs.
2006 Nissan Pathfinder LE
1998 Acura 3.0 CL
"Pleasure in the job puts perfection in the work." - Aristotle (384-322 B.C.)

1985 300TD - Red Dragon
1986 300SDL - Coda
1991 - 300TE
1995 - E320
1985 300CD - Gladys
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