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The patient: 96 F-150, 5.0 auto, 2-WD with flashing check engine light.
The tool: Inova 1403 obd 1 & 2 scanner.
Scanner should power up when connected to port w/ key off. (It does on other vehicles)
User manual sez to check fuses. (Done, all good)
Port cap intact, all pins clean & shiny. Wiggle test of harness behind port does nothing. Fender grounds look good, but batt cable clamps (repacement type) aren't so hot. Engine turns over fine & runs.
Underhood harnesses are good, no hatchet job repairs.
Quite often the power for the diagnostic port goes through the cigarette lighter fuse so check that. If that is good the only other thing I can think of is to check for a bad fuse in an inline fuse holder under the dash.
Sorry I can`t be of much more help.