Looked into it -- turns out blue (15 A) fuse was blown when I did the last jump start.

Replaced fuse, and ABS lamp is no longer ON.

Thanks for the help. I'll post pictures of the W124 OVP later.

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Side question: when I was replacing the black plastic cover, parts of it cracked. I infer it went brittle due to age. I'll replace this later -- any risk in leaving it partly cracked (i.e., it won't keep ALL the water off the relays, etc).