Truck will not start

[simon999]

You need to check with multimeter 12v. When you turn "start" key, 12v has to be on starter solenoid when turning key. If solenoids clicks and there is 12v means bad starter.
If there is no 12v it could be starter relay or ignition switch. You can also check your starter relay input and output with multimeter. If relay input has 12v while turning key no 12v on output meand bad relay.
Thereis old method to check if bad relay, short with wire relay output to the starter, if the starter turns means bad relay.
Also like was mentioned in previous posts make sure you have tight batteries connections, ground connections. Make sure there is no corossion on wires.