1. Find your truck's year: This is crucial. F-100s were produced over many decades with different designs.
2. Consult your owner's manual: This is the best resource. The manual will show you exactly where the fuse boxes are located (there may be more than one) and a diagram of the fuses and their functions.
3. Look in common places: If you don't have the owner's manual, common locations for fuse boxes in older vehicles include:
* Under the hood: Often in a black plastic box near the battery.
* Under the dash: Look on the driver's side, often near the steering column or under the glove compartment.
* Inside the cab: Sometimes in a panel on the side of the dashboard.
Without knowing the year of your Ford F-100, I can't give you a precise location. Please provide the year, and I may be able to offer more specific guidance.