If this is a hard-wired inverter, look for the inverter fuse, which should be in the positive cable that feeds directly into the inverter positive battery terminal. This fuse (by NEC code) should
be within 18" of the battery. If you aren't getting DC power to the inverter, you won't be getting 120VAC power out of the unit.
Solar Tech Energy Systems, Inc.
Victron Solar Components and Inverters, Zamp Solar Panels, LiFeBlue and Battle Born Lithium Batteries, Lifeline AGM Batteries