What could be the issue with my 78 ford f150 with a 351m not starting solenoid just humms?

Is the battery good?

The battery has been showing good

It's either the battery, maybe a bad or corroded connection or the solenoid itself.

Either your battery won't hold a charge ( remove it and have it tested at the parts store for free) and/or you have a bad connection somewhere or your starter needs replaced. You'll need a scrub brush, a 1/2" and a 9/16" box wrench If your starter is bad(usually the brushes wear out) you will need more voltage to make it spin thus it starts with a jump from another battery but not on it's own with just one battery.. The battery might just be tired and not hold enough juice to start the engine especially if the engine is already hot.. Have that checked first as it's free. You could also have a bad connection between the battery terminals(check for green corrosion on terminals) and the starter solenoid on the fender apron or from the starter solenoid to the starter itself. The 78-79 F-150 sits up higher than most vehicles and will endure spray from road salt, dirt, gravel, mud etc. whatever is on the road is splashing up on the starter and on the starter's connection to the battery. Any of these factors can cause a starting problem so I would suggest a process of elimination starting with the battery and working your way down. Connections must be clean and dry. If dirty or corroded use two tablespoons of baking soda in a 16 ounce cup of tap water, mix and pour on the battery terminals. Scrub the terminals with a wire brush or even a hard plastic scrub brush.until they are clean, then rinse with clear water. Then loosen them up and remove from posts. Clean the battery terminal posts with the wire brush (they also make a cheap tool for cleaning off battery posts, available at most parts stores) Let dry then re-attach and tighten them up so the terminals don't spin or move on the posts (dont over tighten) try to start the engine, if still not starting then disconnect the positive cable from the battery again..Then check your connections on the solenoid too making sure they are not corroded or loose. Don't over tighten those as they will crack the plastic solenoid casing easily. Just a little past snug should be fine. Then finally check the connections on the starter making sure they are clean and tight and not corroded in any way. Clean if neccessary. Then hook up the positive battery terminal again and tighten.. If after all that and it still doesn't start, you'll need a new starter. Do NOT buy a rebuilt starter, they aren't worth the trouble, Buy a remanufactured or brand new one. Those 351-M engines are notorious for tearing up starters, especially rebuilt ones. I went thru 7 rebuilt starters in about 7 weeks on my '79 F-250 with the 351-M until I bought a brand spanking new one from Ford. That was 15 years ago and I still have the truck and it still has that same starter on it. Talk about long lasting !!! Unfortunately Ford probably doesn't carry one for your truck anymore but you can still buy a remanufatured one or a new one from some parts stores. Try PepBoys or Advance AutoParts, maybe Napa or CarQuest too. . I know Pepboys stocks parts back to 1968. Forget AutuZone, they only go back to 1992. Good Luck, Kenny / MrblueOval

based on your situation, 2 possibilities. 1, battery has a bad cell. it needs to be load tested. itll show 12.6 but if bad cell itll drop to 10.5 instantly when load test. each cell is 2.1 volts, 6 cells in a battery, blah blah blah. if battery good then bad ground. engine ground to chassis. try jumper cables from engine to battery negitive or a good chassis ground. either you need a battery or to ground the engine to chassis, and of course ensure battery has a good ground to chassis. and if its loose or corroded battery terminals, then slap yourself, lol, jk. :-p.

Thanks guys i got it runnin.battery solenpid and alt. Were bad