I have a brand new starter solinoid on my 88 f150 and the starter is still good but for some reason the only way i can start it is by raisen the hood and jumping across the starter solinoid. Any ideas on what might be the problem

 

The starter solenoid is actually the device on the starter that actuates the starter drive gear. The starter relay is the device mounted on the fender that directs current from the battery to the starter solenoid. There are some differences when you have an automatic vs a manual transmission. We need to know to accurately troubleshoot. When you turn the key to start, , electrically this puts 12vdc on the small terminal of the starter relay, assuming the relay has a good ground, current will flow and the relay will be switched from an open position to a closed position. This will allow current to flow from the battery to the starter, assuming the starter motor also has a good ground and the engine is properly bonded to the frame and the frame properly bonded to the body.

So, if you can jumper accross the relay and the starter operates normally, it can be assumed the bonding of the starter and the engine,frame, body are good. Where your problem lies is in the control circuit of the starter relay. This is where whether or not it has an automatic transsmission or not comes in because if it is manual there is a clutch interlock switch.

Check that the small wire going to the relay has 12vdc when the ignition switch is positioned to run. Check that the starter relay has little to no resistance electrically to the fender.

Let us know what you find.