at 12 seconds of the 2nd video I can see the blue wire hooking up to the heater element.
The black wire looks to be running over to the bottom of the center contactor?

If the other end of the blue wire is going to the heater, leave it off, hook up the black wire and try again.

also at this point with the fuse pulled check that blue heater wire to ground with your multimeter on the ohm or resistance scale. it should read infinity just like you hold the leads up in the air, not shorted like you holding both leads together.