2002 Mercury Marquis Repair Question
Mercury Marquis Engine Problem
I don't have access to a wiring diagram but based on your dandy observations, I'd start by looking at the ignition switch. Back-probe the wires and see if you have only one with 7 volts when it is turned on. If you do, you have a burned contact in the switch or one of the terminals in the connector is overheated. If you find two wires with 7 volts, there's a bad connection before the switch.
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