taillights and brake lights

[nickz84]

I have a 1979 gmc heavy half I changed the valve covers a few months ago and ever since I changed them my brake lights,tail lights and dash lights go out every time i use them I change the fuses each time too then they just go out I havent got any idea why this happens because the valve covers have nothing to do with anything electrical if someone could clue me in as to why this is happening i'd appreciate it very much,I have only driven the truck 2x since I changed the valve covers and I want to start driving it since its finally cooled down here in las vegas.I really want to get this fixed asap so any help is good enough for me