It's not always easy to find, so carefully inspect the area under the dash near the steering column. Some owners have reported it being behind a small panel that looks like it might be part of the kick panel.
A good strategy:
* Look for a small, rectangular panel or door that appears to be removable.
* Use a flashlight. It's often dark under the dash.
* Consult your owner's manual (if you have one). This is the most definitive source. Even a reproduction manual would be helpful.
* Online forums dedicated to 1969 Dodge Chargers. Searching these forums for "fuse box location" will likely yield images and descriptions from other owners.
Remember to always disconnect the negative battery terminal before working with any electrical components in your car.