i have a 95 ranger, and it wont turn over when turning the switch, it starts up fine when you connect the bolts on the sillanoid, ive put a new alternator in it and it didnt help, i beleive that battery was put in backwards and thats what cause this problem but no one can figure out whats wrong

Does the relay click when using the key? If shorting across the relay works, most of the wires are more than likely good. If it does not click with the switch, check for bad wires between switch and relay.

Pull off the small wire with the female plug on the end from the solenoid. This wire should get 12v only when you turn the key to start. If it doesn't then you have bad wire, ignition switch.
If it does get 12v AND shorting the terminals makes the starter turn, but it won't start the car when it's connected to the starter solenoid THEN... the solenoid is bad.

the solenoid was bad
we pulled one off an old thunderbird and it didnt work, so we had given up on that, then we sent it to an auto shop and they put a new solenoid on it and it worked fine