Dash lights, tail lights, brake lights, not working 1965 mustang

Probably either a bad ground (broken wire, rust) or a bad headlight switch. The brake light circuit goes from the stop switch (Located up above the brake pedal) through the headlight switch, through the light bulbs to ground. The tail light circuit goes through the headlight switch, through the bulbs and to ground. The only things that are in common are the headlight switch (Is this the switch you replaced?) and ground.
Not much, but hope this helps.
Have a super day!
Ron