Just thought I would post this because I had this problem and saw a few posts about this on here and a few other forum sites.
I had a bad headlight switch that would shut off the parking lights (and the dash lights) when you clicked it up to headlights.
I know these switches can be expensive so I simply used the headlight wire to trigger a relay to power the parking light circuit! cost me all of a couple bucks for the relay to fix it! only downside is (unless you wire a second relay or add a diode) you will lose the parking lights if you click on the high beams since it is a different circuit.

 

I made my headlight switch do only headlights/highbeams then separate switches to the dash lights, tails and license plate light

that way i could fuse them all, found that the tails were causing everything to short out, so I wired new wires directly to them.