Electrolux Silverado Delux motor doesn't work until turned on side?

Vacuum motor doesn't work until turned on side...sometimes it will try to run but stop. The power is always O.K. to the hose + rug (beater). I took part of it apart to find out the power is good through the disc/ contacts and "on-off" switch. It seems to be some kind of relay (or contact) that alows motor to start. Once started -it will stay on (even when switched off, then on -it will come on! But when unplugged (moved to another outlet) the same roll to side, tapping has to be done to get going again.