Truck won't start but its not battery?

My truck won't start, but its not the battery. Thought maybe it could be the start. Only had the starter for three years. When hooked up it won't turn over but when I connect I use jumper cables and use the fire wall trick and battery trick it stars, but not that loud or powerful. Could it still be the starter? The truck is a 1994 ford f150. I know its not battery because everything is coming on, check the all lights and they are perfectly fine.

I'm not sure if this pertains but tried jumping a lawn mower and then about 20 minutes later truck only started when it wanted too, then stopped coming on.

Starter might be a little weak and having trouble turning everything it's hooked up to. Might wanna go in there and make sure everythin is lubed up like it should be and nothing is jamming. My buddies AC jammed up and it locked up the whole engine.

The battery is still your primary suspect; you're making a false assumption about it. Just because it can deliver low current voltage doesn't mean it's capable of delivering the high current needed to start the engine; that's exactly how batteries wear out. Cheap automotive batteries tend to have around a 3 year lifespan, better ones tend to have around a 5 year lifespan. But there are other faults which can occur (principally with the alternator voltage rectifier) which can considerably shorten the battery life.

If the starter was faulty, it would be equally faulty on your present battery or using the jump cables.

First, try putting the battery on an external battery charger and then get it load-tested. If it passes the test then refit it to the vehicle and check the alternator output at idle and at around 2000rpm. Output should be no lower than around 13v at idle and no more than 14.5v at higher rpm. If outside of those figures you'll need a new or reconditioned alternator, or a tested unit from a pick and pull yard. It's very common these days for alternator rectifiers on vehicles to be damaged by jump starting, and it can affect the donor vehicle as well (never give jump starts! Carry a jump starter pack instead). If you don't check the alternator output then you risk frying your expensive new battery in a very short time.

Just because the lights come on, don't mean the battery is good. It don't take much to light up everything,… But it takes quite a bit of power to make the starter spin the engine.

get a battery condition check,… They're free at most parts stores

Check the battery cables for a good, clean connection, and check the other cable that runs from the engine to the body. And Robsteriark is right, the battery could have plenty of power to run the lights n radio but it may not have the reserve amperage for the starter to turn the engine, that does take alot!