You can BRIEFLYground the wire to see if it moves/pegs the gauge (indicating the sender is probably the issue... either shot or maybe too much teflon tape preventing thread ground), or if it stays at zero (indicating the gauge is shot, or the wire is broken).
The causes of this issue can be a faulty gauge to the need for an oil change. ... Cold weather can also make the oil pressure read low until the oil pump has had a chance to deliver the oil to the engine. I had some a similar issue in my Ford truck that I use for Manhattan 24 Hour Towing, after some inspection there was fuel gauge issue.