Thanks - where/what is the K40 relay? I'll also do a search...

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

It's in the module box under the hood, at the very front. There are a few wires and fuses on top.

Remove it from the car and remove the bottom cover (you will need a screwdriver to separate the cover). Inspect all of the solder joints under a bright light, preferably with a magnifier, looking for fine cracks.