300D Gauge Lights

So after some heavy reading over at Benz World, turns out the rheostat dimmer switch is the common failure on the old 300D’s.

This switch is the one that resets the trip part of the odometer if you push it in.  If you turn it left and right it controls the dimming of the gauge lights from “slightly lit” to “so dark your not sure if they are actually on”.  You can see the wire on this one sticking out, it is part of the rheostat which changes the resistances going to the bulbs.

The way to fix this issue is to bypass the switch all together to where the gauge lights are always on when the headlights are on.  Bypassing the switch does not leave the gauge lights on all the time regardless because the circuit the switch is in is only gets power when the headlights are on.  The way to do this is like so.

Simply solder a wire to connect the two terminals on the back of the switch and viola, gauge lights work again.