Most thumb throttles are cheap garbage, and looking at the Yose site looks like they are no exception. If you have a multimeter and some connectors, wire it up to a ~3V DC source like 2 AA cells wired in series. Check the voltage on the output. Since there are a bunch of variables, I'll leave it to you to find your exact details. Also check that both sides of the plug are in good condition. And finally, thumb throttles are pretty cheap to replace. Grin is my source for all things ebikes related: https://ebikes.ca/ebike-parts/control-stuff/throttles.html