The oil pressure switch sounds like the hot tip to me. He's not talking about the sending unit. This is a switch that makes contact when there is oil pressure. You can tee into the outlet where your sending tube is.

"It's just a phase. He'll grow out of it." Mama, 1964

1956 Chevy 1/2-ton 3100
1953 Chevy 6100 "The Yard dog"
1954 GMC Suburban Now with a new proud owner.