ESCORTCOSWORTHUSA : Check if it has fuse link tail wires that go to the battery. I spent days checking everything and doing exactly the same as you have. New Battery, New Alternator, only to find out it was the fuse link wires. My car is very low mileage and is kept in dehumidified storage, so just coz the car is well looked after dosent' mean these don't corrode. And the worst thing is, they look ok when you look at them.

I changed all three for 35amp wire, and put an inline fuse in each circuit (45amp) and I now have full power back to everything.

Jim