Truck was hacked up to change brakes. Ran before, now won't stay running

The security light on the dash sounds like an anti-theft system is not being disengaged, very possibly because of a problem with your key communicating with the immobilizer system. This could be a fault of the key or corresponding immobilizer parts. If your key fob is dead, it's also possible that other anti-theft systems are not being disabled. Is there any aftermarket system attached to the vehicle. You definitely have clues here. I don't know how changing the brakes has anything to do with it, or what "hacked up" means.