Do you have any alarm system installed? Like a starter kill. Sometimes you can have power to everything except the starter. If no alarm then check the hot wire that powers the solenoid. If the wire is hot,(remember the key has to be turned to power this wire), then its within the starter. Maybe a ground? Maybe a short in wire to starter? You could do a continuity check on both the ground and the hot wire. Just ground your multimeter and touch each wire. Should only have continuity to the ground wire. DUH! If you have continuity to hot wire then you have a short. If all is well, then try a continuity check from where your hot lead starts to the starter. It could also be that the solenoid is bad and needs that much voltage to power it up. I mean it only works with a jump from terminals. Sometimes solenoids just get weak. Good Luck. I hate starters on most cars. Im not a big fan of solenoids on starters. I like em on the firewall. Makes for easy diagnosis.