"what should the voltage be at with the engine running?"

it's not that simple. It depends on your battery's present state of charge and the electrical drain on the system at that moment. The proper way to check an auto electric system is to use a device which tests loads (amps and volts) like a Vat-40 which is what most dealers and better auto shops have. If in doubt, don't guess, have it checked out by a place with proper equipment.