lights do not turn on when i put the keys in the on position

Okay, so i have a really weird problem going one with my 3/4 ton truck. I have recently just replaced a fuel and water pump also a fuel filter. i have noticed that sometimes my lights do not turn on when i put the keys in the on position on this year model truck the lights turn on automatically when you put the switch in the on position. well after messing with the keys and turning the switch on and off the lights will turn on and the truck will start and that is the only time is will start if the lights do not turn on the truck will not start. this is the first time this problem had happened with any of the vehicle i have owed and clueless on what it could be. need a little help on what the problem could be it will be.