Salesforce: Campaign Influence with Primary Campaign Source Model

Primary Campaign Source Model (or Salesforce Model) is the only OOTB available model in the customizable campaign influence if you do not have MCAE/Pardot, but you can create your own model as explained here.

How does the system add a campaign as Campaign Influence?

1. Primary Campaign Source

When the Primary Campaign Source field is populated in the Opportunity, it will be auto-added as Campaign Influence, even if it does not fit the Auto-Association rules and time frame defined. The Influence % will be 100%.

Changing Primary Campaign Source will set the previous campaign to 0% and the new Campaign to 100% influence. The same applies if you delete the Primary Campaign Source from the Opportunity; it will be set to 0%, but make sure the Record Preference is set to "All Records" in the model setting.

2. Opportunity Contact Role

The Contact added to Opportunity Contact Role must fit both Auto-Association rules and Campaign Influence Time Frame. The Record Preference on the Campaign Influence Model Setup must be set to "All Records"; the Influence % will be 0%. 

If you set Record Preference to "Records with >0% Attribution", the Campaign Influence record will not be created, as it is 0% influence.

So, if the Opportunity has Primary Campaign Source and Opportunity Contact Role link to different Campaigns, all Campaigns will be added as Campaign Influence. The same applies if the Contact in Opportunity Contact Role links to multiple campaigns that fit the auto-association rule; all Campaigns will be added as Campaign Influence. They can be from the same or different contacts in the Opportunity Contact Role.

Reference:

• Salesforce Platform: Implement Custom Campaign Influence Models with Apex Triggers