"I think the eletric fuel pump power circut is wired so that oil pressure is required for the electric pump to run."
That's NOT true with those vehicles. The fuel pump relay (operated by the 'puter) and the fuel pump oil pressure switch are in PARALLEL.
The fuel pump will run as long as the 'puter keeps the relay energized 'cause it knows the engine is cranking or running OR as long as the oil pressure switch remains activated.
The oil pressure switch serves as a fail-safe for the relay, in the "ON" mode, meaning if the relay or relay circuit fails the fuel pump will still get energized, but after a longer cranking period 'til the oil pressure switch gets activated.
I know that flies in the face of conventional wisdom, but that IS how GM set these system up in that era. The oil pressure switch is redundant, and the vehicle will operate normally without it, AS LONG AS THE RELAY AND ASSOCIATED CIRCUITS ARE PROPERLY FUNCTIONING.
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