[mike in tucson]

It is important to know the current capacity of the oil pressure switch. For instance, the stock GM 5.7 switch is packaged with the oil pressure sender and has very little current capacity...it is intended as a signal to the ECM. Some builders route the electric fuel pump circuit thru this switch and, similar to an overcurrent situation in a relay, burn the contacts. Such suggests for troubleshooting (like everyone is telling you) that you use a jumper to bypass the oil pressure switch.
By the way, the stock GM oil pressure switch is used to prevent the engine from starting until the minimum oil pressure is reached (3psi I think). It is a signal to the ECM that it is OK to start. An inertia switch is used in case of a crash to shut the fuel pump down to prevent fire.