wiring diagram for trane air handler

does anyone know where i can get a wiring diagram for a very old trane air handler?the unit is a closet air handler made aroud 1977.i do not have a model number because the tag has been ripped of.it was made before they started making the base twv air handlers of the mid 80's. the unit has the coil on top,then the fan,then the electric heat kit (downflow) i know this is alot to ask without a model number,but i am trying to troubleshoot this over the phone with a family member that is out of state.any assistance would much appricated. thank you