/home/katrin/koha-dev/etc/zebradb/ccl.properties:

#Record-linking       1045                                  7xx$w, 8xx$w
Record-control-number 1=Record-control-number
rcn Record-control-number

/home/katrin/koha-dev/etc/zebradb/marc_defs/marc21/biblios/record.abs

melm 770$w      Record-control-number
melm 772$w      Record-control-number
melm 773$t      Host-item
melm 773$w      Record-control-number
melm 774$w      Record-control-number
melm 775$w      Record-control-number
melm 776$w      Record-control-number
melm 777$w      Record-control-number
melm 780$t      Title
melm 780$w      Record-control-number
melm 780        Title,Title-former,Related-periodical
melm 785        Related-periodical
melm 785$w      Record-control-number
melm 787$w      Record-control-number

/home/katrin/koha-dev/etc/zebradb/biblios/etc/bib1.att

att 1045    Record-control-number