Slick 60's

Newly acquired 66 2wd f250
Pretty unmolested barn find
Trying to get everything to work
Here's what I got....
Headlights work high and low
Taillights and and brake light only work when turn signal lever is up or Down position
When you center "shutoff" turn signals no Taillights or brake lights
When you turn on headlights. It cuts off Taillights
Cab light works ok

Advice
Vehicle never had anything after market wired in and harness looks unmolested and all fuses look un blown and replaced all bulbs

Thank you
Brian Stankowitz

Same old standard advice; start by checking all grounds. Use a jumper from individual bulb sockets to ground to test if needed. It sounds as if it's trying to ground through other circuits. If that proves false, look for bare wires contacting each other.
Paul