Any tips for electrical problems?

[lt1tyrell]

I am terrible at solving electrical problems but here goes...66 c10, fairly original wiring but it looks like many years ago somebody did some hacking of the wiring harness, added some old 4 way flasher kit etc. So the truck had headlights but no taillights or brake lights. I replaced the light switch and that didnt help. I also looked at the connector for the switch and compared it to another 66 chevy that was close by. The purple wire was disconnected on mine so I put it back where it is supposed to be on the switch. Now I have brake and tail lights when the switch is in the "park light" position. As soon as I pull the switch to headlights, the tailights and brake lights do not work but the headlights do! I am sure this is way too confusing and is something that has to be looked at in person but any tips are welcome. I figure I might have to hire somebody to fix this problem because like I said I get frustrated and I am brutal with electrical problems!