Does cable diameter make a difference

[street]

My +21drivers side window does not work properly, using remote power source with a switch i have rigged up, window goes up an down all day long.

I have tested car wiring and i have complete circuit when operating switch up or down.

Connect terminal together and nothing happens, on observation i have sparks between the negative cable when holding them together which seems strange? the only other factor is I upsized the negative cable to about 2.5mm from connector to door motor whereas the cable is about 1 / 1.5mm from switch to connector.

Would this make a deference?

thanks

[The Veg]

Try a direct, large-diameter earth-lead straight from the motor to a chassis bolt, no connectors along the way. This took my windows from being weak and sluggish to moving with authority.

But it sounds like some good basic electrical troubleshooting is needed.