Please call toll free after 9 AM CST to 1-877-263-7860 and ask for Mark to order a Parts and Wiring Diagram for $15.00 if you don't have those.
That will show you the parts and wiring. The filter slides in at top and top should be open to filter and there should be a square cut out in wall above furnace with a grille over it.
The return air is pulled through the grille and down through the filter.
There are 3 disconnected wires, but unsure where they go w/o wiring diagram in front of me, pics were fuzzy up close.
Your sequencer controls the elements and blower in heat-auto mode.
Would need to know if it is getting 24vac to bottom terminals from t-stat.
Some people are Humbly Grateful, while some are Grumbly Hateful.................... Which one are you ?