1986 f150 won't start. just a buzzing from solenoid. changed solenoid and till no start. Any help would be appreciated. won't turn over , battery is fully charged.

Check and make sure all the battery cable connections are clean and tight. Make sure you've got good grounds. See if you can turn the engine over by hand ( you never know :D ) . If you are getting some noise when you turn the key but it won't turn over and the battery is good , the grounds are good, the solenoid is good and all the connections are good then you should probably pull the starter and have it tested at a parts place.

Have you tried jumping the solenoid? That's something else to try. Just make sure the truck is in park if it's an auto or in neutral if it's a manual( with e-brake on or wheels blocked ) .

If you turn the key and don't get any noise at all then you should check out the ignition switch, clutch safety switch ( if a manual transmission ) or the neutral safety switch if you have an automatic.

prolly gonna pull the starter. jumped the conections on the solenoid and nothing. Engine spins fine by hand. thanx, just new to fords, always been a chevy and yota guy. decided to try something new and a $200 truck isn't bad

The buzzing may be the starter motor spinning without the bendix engaging. If its dirty and oily try just tearing it apart and cleaning it up.

mine did the same thing and it only happened when the battery didnt have enough to crank the motor and it turned out that it was shorting and discarging the battery because of a bad alternator

Before you pull the starter, run a jumper cable from the hot lead of the battery to the hot pole on the starter and the ground to the body of the starter. Make sure its in Park or Nuetral. I'm betting on a bad cable or a bad connection. The buzzing is the starter relay undercurrent not allowing it to deploy. Cables and terminals can look fine from the outside, but can be rotted through somewhere inside the insulation and not passing current. Also, a loose connection at the block ground or the starter will not pass enough current to throw the relay.

bad starter and battery. old starter was fried and battery would barely hold a charge