Hopefully one of these sites will work for instructions:

W123 Service Manual
https://www.startekinfo.com/StarTek/outside/12265/?requestedDocId=12265

CD1
http://mb.bolinko.org/15/w123-mainmenu-50/w123-dokumentacja-cz-1-mainmenu-59.html
CD 2
http://mb.bolinko.org/15/w123-mainmenu-50/w123-dokumentacja-cz-2-mainmenu-83.html

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84 300D, 82 Volvo 244Gl Diesel