In my case (same symptoms), definitely diagnosed as a bad relay (stuck/welded closed/on). This is a common failure mode for relays in general. I disassembled the bad relay to see firsthand. The corroded contact with charred carbon deposits confirms the failure mode. The new/shiny/clean contact is an example of an unused contact surface. BTW, the Ford OEM part has been upgraded since 2017 and is rated for 40amps. Beware aftermarket parts lacking a rating or possessing a lower rating, e.g. “25 amps”.
