Phil, I don't believe trusses need load bearing walls. I believe they are self-supporting, but I may be wrong. The rest of the information is correct. If the ceiling joist run North and South, then the load bearing walls will run East and West. They support the ceiling joist. Generally. If the house is on a slab and you have the blueprints, there should be a poured beam in the slab under all load bearing walls. If you're uncertain, almost any contractor would be able to tell you and even though it is a load bearing wall there are ways to remove it. Hope this helps and be careful.