I would use a relay and feed the control circuit from the park lights. Then a fused power supply to the relay for the lights. Then you dont have to worry about extra current draw through the light switch.
Do your park lights burn when the headlights are on?
If so, this should work. If not, I'm not sure, cause they would only light when the park lights were lit. You could add a 2nd relay controlled by the headlights if needed. Then they would light if either were on.

"Do not walk behind me, for I may not lead. Do not walk ahead of me, for I may not follow. Do not walk beside me either. Just leave me alone, you're starting to freak me out."

1957 GMC 150