Heres as voltage meter I have thats under $20, under $15 if you shop around:
Gardener Bender GDT 3190
A good investment for this hobby. These can be found at the local hardware store as well as Amazon, Walmart ETC online.
OBVIOUSLY given the current circumstances, it may be difficult to get one at this time with stores closed and only "essentials" being sold online.
In the meantime. I'd run that same locomotive with the long string of dump cars around for 10 minutes, then check for heat in that area. Your 1 switcher by itself probably isn't a big draw on power.