Why wont my truck start could it be the starter I changed the battery

make sure battery has a full charge and connections all good? As far as the starter, note starter relay in diagram. Unplug the relay, use jumper wire between cavities 30 and 87, the starter motor should crank the engine. Make sure transmission is in park or neutral and parking brake is set. The vehicle can't move. With key on, key on is just where the dash lites come on, helper with foot on the brake. The best you can hope for, is vehicle will crank and run. The least you can expect, the starter motor will crank the engine, hopefully. Sometimes when battery voltage is lost, it might effect your security system? If you think starter motor itself is the issue, sometimes you can remove starter motor, lay it on the ground, hook up jumper cables properly from starter motor to battery, the starter motor should kick out the drive gear and spin. I can only help with testing. good luck