micky wrote:

I thought it would be the other way around, that with no connections,
electrons would pile up at one output screw and somehow make it harder
to turn, and with a connection it woudl be easier. But that clearly
wasn't it

Nope. In diesel-electric locomotives, when they are stopping the traction
motors are connected to a large resistor bank to aid in braking. Some of the
more modern systems store the energy or feed it back into the power system
if it's an electrifed train but the old junk I worked on just made very hot
resistors.