My 1976 f250 with a 360 is showing low oil pressure at idle. The gauge comes up with rpms? Truck is new to me. Should I be worried? Gauge shows all the way down at idle.

 

The better thing to do is get a pressure gauge and connect it to the oil sending unit port and see what the pressure actually is. Many engines have no problem with 10-15 psi at idle.

 

Don't trust the dash gauge. If you indeed had low pressure, the engine would be noisy. If you have 10 psi for every 1000 rpm, you will be fine. I would install a new sending unit and an electrical gauge to match inside the cab. Stewart Warner makes good gauges.
I am curious what your exact pressures are at idle and at 2000 RPM? What weight oil is in the engine?