I’ve been roped into fixing a few Personal – type EVs lately, and found this, via ElectricScooterParts.com, complete with procedures for testing throttles and stuff. Check it out. Although it’s pretty specifically for scooters, there’s a ton of stuff that cross-references to e-bikes too. The troubleshooting logic tree applies to almost any EV out there, too.
Besides that, they’re a great source for random scooter stuff, too.