Just a comment (I am still getting to know my 300E)
6 yrs ago, my instrument panel was acting crazy - gauges moving wildly (sometimes working correctly), it started to become more of an issue, and if I recall correctly maybe a low battery, it turned out to be a voltage regulator/brushes. You may want to check it (just to get it out of the way) part is about $30 (others suggest to keep the old part as backup).

see this other post 300E electrical mystery

I have also noticed a random ABS light on / off for the past two years or so (topic for a separate thread) - may be related to the OVP Relay (which may also be a solution).

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89 300E - 240k +

Thanks for all the suggestions...

Yesterday while working on the 500E, my father suggested replacing all of the fuses... they all LOOKED FINE & a few were already copper... no breaks found... I twisted all of them to ensure contact...

I was just about to leave for the dealer to pick up a Brake Light Switch when I read through the suggestions here on the forum... emerydc8 suggested changing all of the fuses as well... so before heading out to the dreaded dealer, I figured... what the hell... it took FOUR parts stores to gather all the necessary fuses (these are getting harder to find apparently)... Took them home, put them in, & planned on going straight to the dealer... NOT NECESSARY.

COMPLETELY FIXED... I haven't checked/cleared the codes yet, but everything back to normal... I'm not sure which fuse or fuses caused the problem, but wow, it led to a lot of systems showing errors & malfunctioning!

Thanks again all... time to go enjoy a Cuban lunch on the money I didn't have to spend at the dealer today! =)