my head lights come on when key is on no brake lights ,turn signals or brake lights . put new fcm on now head lights are off but engine will not stay running.

 

If you haven't tried it yet, I would have to say you need a fuse box. If you get one from a boneyard, it must be from a diesel. The fuse box from a gas engine truck is internally wired different. The brake lights or the lift pump will not have power. I know this from experience.