Hello All...
1992 500E, starts fine, brakes fine, but...

-at first touch of brake ABS & ASR lights come on & stay on
-instrument cluster DEAD except for illumination... ALL dials dead (RPM, Temp, Oil Pressure, Gas)
-Relay 201.821.00.47 buzzing loudly
-#6 Pin Error Codes: 13 (Stop lamp switch), 30 (CAN data bus to EA/CC/ISC control module interrupted), 32 (CAN data bus to DI control module, Left DI control module, Right DI control module interrupted)

Am I right in assuming I should start by replacing the Brake Light Switch?

ALL Fuses appear to be fine...

201.821.00.47 is a multi-purpose relay that can be had for about $60-$70.

But if I were you, I would change out all my fuses with the copper fuses, just in case any fuse happened to be bad and it wasn't readily apparent from looking at it. It would be a cheap fix. If you are in a rush, I think Autozone has these in the Bussmann brand for about $15 for all of them.

Also, check the Delco-type fuses in the base module (that's under the lid that says battery in trunk). You will see them when you remove the lid.

The brake light switch is a common problem and considering the low price, it too would be something to consider before going on to more expensive possibilities. If it has never given you trouble in the past, it probably eventually will anyway.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles

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! =)