No power at key

OK, let me confirm, you checked last:

One probe on the battery positive

other probe first on one, then the other ammeter terminals

AND lights are on "and dim" and it shows zero volts?

and still no power things like heater blower, from the key?

If this is so, we need to confirm a couple of things:

THIS TIME clip one meter probe first to one, then the other ammeter post

Clip the other to a good ground.

Confirm that lights are dim, and measure this voltage

Try the key in accessory, run, start, while watching the meter, and try accesssories like wiper, heater blower, etc.