It's hard to comment on all w124 issues so I'll just put in my two cents....a post facelift w124 (1994-1995) is going to have different characteristics than a late 80s/early 90s 124 (nissanzx1's comment on the harness is a big one), so just be sure to keep that in mind when doing your research on which years you're looking at purchasing. I have a '95 so I can't comment accurately on the '86 you're looking at.

Keep us posted and good luck!

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1995 E420
1998 SL500 Sport
2009 E350 Sport
1995 S500 Coupe
1992 500 SEL