RepairPal Certified shops can diagnose and repair your 2006 Toyota Tacoma. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
Here is a link to the diagram:
https://www.autogenius.info/toyota-tacoma-second-generation-mk2-2005-2008-fuse-box-diagram/
Information can be found in owners manual as well .
There are certainly more possibilities for heater malfunction. Good luck!