If you don't have a multimeter, I'd highly recommend getting one. Even just the cheapest multimeter (DMM) available at your local "harbor freight" equivalent store is pretty useful for testing and troubleshooting ebikes. Around here they can be had for less than $5 - $10 USD, typically. They're not great at that price, but they'll generally do what you need to with this sort of thing; I have several of that type that i use for anything that doesnt' really need precision (if I screw up somehow and damage it, they're actually cheaper than just a fuse for my really good DMM). $50 USD gets a pretty decent multimeter, and $100USD gets a nice one...but you will probalby never need anything that fancy.
As examples, this one
https://www.harborfreight.com/11-function-digital-multimeter-with-audible-continuity-61593.html
is $23 USD and has some features that make it more useful than this one (but not features you *need* for basic testing):
https://www.harborfreight.com/7-function-digital-multimeter-63759.html
which is only $4 USD (and is just like half a dozen of them I have around here, that do all the basic stuff for testing ebike things, but sometimes take a bit more creative setup to use for certain things).
This one
https://www.amazon.com/Fluke-101-Multimeter-Resistance-Capacitance/dp/B00HE6MIJY
doesnt' have much more in features (less, really) than the first one above, but it's a much better meter if you needed accuracy, durability/reliability, etc.
This one has some more stuff, but costs more than twice as much
https://www.amazon.com/Fluke-107-Current-Handheld-Multimeter/dp/B00HEAMMIC/ref=sr_1_9?dchild=1&keywords=fluke+77&qid=1610944517&s=hi&sr=1-9
Some cheap under $5 Amazon meters (that I know nothing about):
https://www.amazon.com/Ranging-Digital-Multimeter-Voltmeter-Tester/dp/B08CN7J9M5
https://www.amazon.com/Kaczmarek-Multimeter-Continuity-Voltmeter-Ohmmeter/dp/B08R9V5CYY
My "best" DMM I use for general electronics stuff is the couple-decades older version (77-IIIA) of this
https://www.amazon.com/Fluke-77-IV-Digital-Multimeter-Yellow/dp/B000U8WQ4U
but it's definitely overkill for simple ebike troubleshooting.
However, it and a two much older Flukes, 8020A (handheld) and 8000A (bench) IIRC, (from the late 1970s?) still work despite being dropped, banged around, accidentally launched across a room (and a yard) by tripping over test leads, etc., many times over the decades.
Can't say that about any of the HF meters I've had. (of which I have a few that are saved for parts to fix others if I ever need to).