Well....there could be several explanations.
First off, you said you just bought this truck. Are you sure you know how to use the cruise control? Press the ON button and then press the SET button.
Second. The turn signal could just need a bulb replaced.
Third. You should NEVER see a 6.4 glow plug light come on unless it is extremely cold outside. I live in Texas and it has never been cold enough for my light to come on.