So....my testing ability is at fault. >


Yes ...that was my suspect reading your complaint and the logic for disconnect of feed to F15.
So , you want to confirm your test lamp across the battery terminals and then go back to F15 when you have validated the lamp. If no V at F15 again, then I want you to use Battery neg as ground leg for test lamp instsed of chassis ground...that will confirm a good ground for test .
I do not suspect this as your problem b/c you have no fan with F15 input disconnected.
but we want to verify test lamp before going to the 3 wire connector at firewall.
F15 feeds the 3 wire connector , and that in turn feeds the regulator/blower assemby, but we want confirm up there first before next test b/c the next in sequence test involves getting down to blower compartment.

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A Dalton