When my headlights are on, my passenger side brake lights don’t work. I checked the 15 amp fuses but all were fine...is it another fuse?

 

Check and clean your grounds for the rear lights. They can be found behind the drivers side rear plastic panel.

 

The ground for the passenger's side may be behind the other side panel.

 

Check your headlight grounds, too.

By the way, "Check your grounds" means find them, take them apart, clean them down to shiny bare metal, and reassemble with dielectric grease.

Then use a multimeter to check the resistance from the ground connector in the socket to the battery negative post. You need to verify the whole circuit.