There's no relay, Nick. At the bottom elect. connector, there are 3 pins, designated 19, 18, and 17. You should get b+ (12v dc) at the far left pin (19) on the electrical connector when the switch is turned . Or, a test light should light up if that's what you check b+ voltage with. Use the other 2 pins for ground. While leaving one test lead attached to 19,The middle pin will be used for ground when you check the fast speed and pin 17 will be used for ground when you check slow speed. I hope that makes sense.
Since you've already replaced the motor,
If no voltage, either a ground is bad, or the 30 amp fuse, or wiring from fuse to the connector.
If voltage is ok, you probably have to remove the cowl and look for a binding drive rod, or the crank arm is loose in its connection to the rod.
(I think there's a reset-type circuit breaker, but it's part of the motor internals.)