Data Loader for Partner Site Users

For Partner Site Users to use Data Loader

1. Grant API access by checking API Enabled on a custom Partner User profile or permission set. 
2. Download and Install Data Loader on Github. (forcedotcom / dataloader)
3. Set 'Data Loader' Server Host to either Production https://login.salesforce.com or Sandbox https://test.salesforce.com
4. The Security token must be blank since Partner User Licenses do not have security tokens, and they are not necessary for this license type.

Note: You can remove 'API Enabled' from the Profile or Permission Set  at any time to prevent Partner Site Users from logging in using Data Loader.