1993 Chevy Astro Tail Light Issues

Hi, I bought my 93 Astro extened cab used. Recently I noticed my turn signal was not working. When I checked my brake lights also failed. My emergency flasher work, but when I turn on the headlights/taillights the flashing stops. Is the bulb supposed to be the taillight and the turn signal? If so, what could be the issue. I replaced the bulb sockets/holders because of quite a bit of corrosion, but still no luck with the brake lights and turn signals. Any suggestions? The van is barely worth 500 bucks, so I cannot take it in for major repairs.