it's always best to include the year and vehicle make in your title, many will give info without reading what vehicle you have.
the 240D does not have the junction block on the fender. the alt connects directly to the starter harness.
just follow the wires from the alt, to the next junction, at the starter, and clean all connections.
you could also have water dripping on the ground block inside your dash, causing voltage issues with the lights on your dash.

dim lights with the key on, is a ground indicator, so I'd check ALL connections for corrosion...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!