1984-f150 tank switch location

i have just acquired (was given) a 1984 f150 to get back to running order after it has set for 10 or so years. The problem I am having is it has 2 fuel tanks and a propane tank (it is duel fuel, after market i think). I can not find a gasoline tank selector switch (i found the one to go from gasoline to propane) on the dash i was told it should be near the lights but i can't find it. Did they still use manual valves to switch tanks in 84 or link the tanks maybe? i have never driven an F-150 before so i am clueless.