My 1984 300D has developed an annoying quirk. All seems to be fine during daylight, but when I turn on the headlight switch, the gas gauge pegs out at full, the temp. gauge pegs out in the red zone, and the high-beam,
seat-belt warning light and glow-plug light all come on along with both turn-signal indicator lights. At the same time, the panel lights no longer come on with the headlights, and rotating the panel light dimmer causes all these unwanted lights to go on and off depending on its position. Is this a ground problem, a dimmer switch problem or what? Any help would be greatly appreciated.

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kjcalhoun
Bosch certified DFI Tech
20 years experience
MBCA Member, Southern Stars
1984 300D
1985 300CD

It sounds as if the dash illunination is trying to ground its self through the instruments. Check the grounds.

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Benzmac:
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Benzmac,
I just pulled my dash panel out and released the speedo cable so I could see behind it. As I move the panel in and out of its position in the dash, the panel lights will go on and off depending on where I position it. When the panel lights come on, the dash indicator lights return to normal operation and I can adjust the brightness of the panel lights with the dimmer knob. Unfortunately, when the panel is fully in the dash is when I get the wierd indicator lights. Any suggestions?

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kjcalhoun
Bosch certified DFI Tech
20 years experience
MBCA Member, Southern Stars
1984 300D
1985 300CD

Try adding a ground wire to the metal portion of the speedo housing.
The reason for adding a ground wire is to see if the ground circuit that comes thru the electronic speedo is broken. Very common if the clock "hot" wire touches the metal housing.

[This message has been edited by M.B.DOC (edited 10-20-1999).]

Check the circuit board, on which these gauges are mounted, for burns or breaks in the circuitry. You will need to remove the cluster then remove the gauges. Check for continuity of the ground circuits. Solder any breaks in the circuits. Hope this helps.