The components carry a relatively high current which is hard on contact tips in the switches and relays. It could be the switch, relays, worn motor brushes or poor connections. If you were to use a troubleshooting approach vs a parts replacing approach I would check at the motor for what you have lost. Did it lose positive to the motor or did it lose negative. You could see positive and negative at the motor yet not have amperage available because of resistance in poor connections or burned/worn contact points in the switch or relays.
Could very likely be a switch or relay