Oil light not working

Take the sender wire and clip it to a good ground. Light should come on with the key in "run" It is a "series" light, circuit path is sender "ground" when switch made, through sender wire, through bulkhead connector, through cluster connector to one side of lamp.

Through the lamp other side is connected to switched 12V from ignition switch.

And yes.........with key in "run" you should measure battery V at the sender wire to ground