Problem solved: Intermittent high beam headlights (both)
Side benefit: brighter headlights.
From around 1996 to 2000 the W463 came with a turn signal switch borrowed from the E-class, which had computer module driven lights. The tiny internal contacts which were meant to send a logic signal to the module (on the original car) were re-purposed to switch 120W to the high beams.
Needless to say, they don't last long. One night you will be rocketing down a twisty road and when you switch to the high beams all you will get is inky darkness. Not only that, but the low beam contacts will burn out not long after that.
The solution is to add headlight relays, just like the factory should have. The attached PDF shows the wiring diagram and parts required to install the relays into the factory relay rack under the glove compartment.
I have found that even a "burned out" high beam switch will correctly trigger the relays. So, if your switch has failed you might want to install relays first.
Here is a very dusty picture of the actual install. Most of the wire terminations can't be seen, sorry.
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