I agree with PKRWUD. The line to the charcoal canister is just an evaporation line and it helps to less the pollution caused by fuel evaporation from the tank. If you disconnect it, dust and other crud may get in the tank if you leave the line open to outside air.
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previous name: 84stangLX
'84 Mustang 5.0 LX
my LX
'89 Mustang GT
my GT