My 99' F-150 has recently failed to start by turning/clicking key over until approximately 10-15 times....this has happened on several occasions after it seems the problem went away...is it possibly a starter relay problem on firewall, or at starter itself...or possibly a faulty ignition switch?

 

Not sure about your starter design but I imagine its similar to my year. Anyways, the reason I ask is, that my model year, the wires are designed in a horrible way that allowed to be dripped on alot by water and eroded away by dirt, stones, etc. The wires could be worn through and only short through on lucky attempts. I would crawl under and look at the wires, should be fairly easy to spot either lots of corrosion or worn wires. I don't know a real solution to that, because I believe the terminals are inside of the starter housing.