I have had this exact problem myself on several occasions. All three times it was corrosion in the connections to the light assemblies. You need to unplug the connectors and clean both the prongs and the holes with sandpaper. For the holes roll up the sandpaper grit side out into a small cylinder, ream, then blow out the connectors to remove excess grit. It has worked for me in the past. I'm guessing your problem is the same

'87 300SDL 278,000
'94 SL500 50,000

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jcciem
'94 SL5000 60,000
'91 350SDL 545,000
'91 350SD 197,000
'00 E55 AMG 77,000