No start by key,but works when jumped.Help!!

If there is any power at all inside the car, Horn , Brake lights, etc.., the fusible link and stuff is good. Everything else gets its hot through the ignition switch. If you turn the switch to the on position and signal, radio, wiper fuses dont get hot, the ignition switch is the most likely culprit.
Only power to horn Red.Thanks.I have read your responses and am glad to see you chimed in.You really know your electrical,which I only know some basics.Thanks I,ll try switching ignition,cause I have a spare with keys.