Queries :: Variable In A Select Query?

Im trying to pass a list box variable in a select query. I understand you cannot pass a variable directly but have to pass it through a function. I may be wrong in this, but whatever I do I cannot get it to work. Here's my code:-

Public Sub GetEquipment()
List387.RowSourceType = "Table/Query"
List387.RowSource = "SELECT findequipstr() FROM Equipment"
End Sub

Public Function findequipstr() As String
If IsNull(List371.Value) Then GoTo function_end
findequipstr = List371.Value
function_end:
End Function

If I MsgBox(findequipstr()) within my Getequipment function, the variable is messaged,