Which System Should You Integrate First?

The short answer: whichever system your team already opens by hand to answer the same question every day. Not the biggest one, not the newest one, and not the one whose contract is up for renewal.

Follow the manual lookup

There is usually one question that gets asked constantly and answered by a person switching windows. Has this order shipped? Did this invoice get paid? Is this lead already a customer?

That lookup is the best first integration, because the value is immediate and obvious, the correct answer is already known to somebody, and you will find out within days whether the link works. Compare that to starting with a full ERP-to-CRM synchronisation, where the first proof of value is months away and everyone has to take the benefit on faith.

Read before you write

Reading from a system is dramatically cheaper than writing to it. A read that goes wrong shows a stale number. A write that goes wrong corrupts a record that other people depend on, sometimes silently, sometimes irreversibly.

So sequence it: pull data out and prove the mapping is right in a place where mistakes are visible and cheap. Only then start writing back — and when you do, write to one field, watch it, and expand from there.

Decide who wins before you connect

Two systems will disagree. The CRM has a phone number the ERP does not; the marketplace has an address the ERP overwrote last week; the finance system thinks the account is closed.

Before any connection is built, write down which system is authoritative for each field. Do it afterwards and you get a sync loop where two systems overwrite each other in turn, which is much harder to unpick than it is to prevent. This is the least technical part of the work and the part most often skipped.

Sequence, not a big bang

The instinct is to map everything and build it all at once, because a partial integration feels incomplete. In practice one link that people trust changes behaviour faster than four that are nearly finished — and it funds the next one politically as well as financially.

There is a practical test for whether a link is finished: has anyone stopped doing the manual lookup it replaced? If the spreadsheet is still being updated alongside it, the integration is not trusted yet, and adding a second one will only spread that mistrust further.

We have written before about what has to be true before any of this starts, in preparing your data for AI. If your systems are not talking and you are unsure where to start, our data integration services begin exactly here — with the lookup somebody is doing by hand. Book a free audit and we will find it.