I just installed a keyless entry system in my 89 420SEL. I used the system shown over on the W126 coupes web site.
Great price & it works as it should. Only one minor difference in my 89 SEL's wiring harness for the pneumatic lock modual compared to the 85 SEC's.....the red/black wire described on the
SEC is red/white on my SEL. No biggie, just thought I'd share.
Thanks Jim Ham for supplying this info for all to see!
Now I don't have to worry about scratching my doors with the keys anymore.