This sounds like a battery that isn't putting out it's full load of cranking amps anymore. However, when you turn the key to "start" a relay should automatically turn off all of your electrical devices. So I would start there with the starter relay.
You can only do this in park ... Turn off your truck ,apply the parking brake and turn your truck back on .
Park on a level surface and measure and mark 25ft. forward of the truck. Wait for condition of low light. Start the truck's engine and turn the headlights on, set to LO beam. Adjust the headlights so that the brightest part of each beam hits the ground 25 ft directly ahead of the lens (not to the left or right.) You may need a #2 Phillips head screwdriver to turn the adjusters.
start by checking your fuses.
push the emergency brake pedal down ONE CLICK
what is wrong when the truck just turn over and want start.
You can only turn off the headlights by applying the emergency brake. When the emergency brake is on, the headlights will not light. Otherwise the best of my expererience is that they are on all the time. If you have remote start, put the emergency brake on before you leave the vehicle and when you remote start it, the headlights will not be on, but the driving lights (if switch is on) will be on as well as the parking lights.
The only way you can completely turn off the headlights is to push in the emergency brake slightly, then start the truck and leave the emergency brake on the slightest setting, and the running lights will stay off. Obviously the brakes will be slightly engaged, but you can adjust the emergency brake so the first click doesn't engage the brakes.
turn the key? no start? check the battery connections. clean them make sure they are tight turn the key no start? turn on the headlights if you have bright headlights, the starter may be the issue. if you have no headlights, look at charging the battery after battery charge turn the key tries to start or clicks probably a dead battery if the car turns over and just won't start do you have gas? If the car turns over and tries to start that means the battery and starter are good now you need to find out why you are not either getting spark of fuel.
A blown fuse.
Fuel pressure? spark?
Check your fuel filter
There are a couple of different times when you'd turn off your headlights. You'd turn off your headlights when the car is off for example.