I used a Variac and 2, 8ohm 10watt resistors on the output with volt meters across them. Short the inputs. Take the covers off. As I easy up the variac, I watch the meters, sniff around and look for smoke. Now I would use an infrared thermometer. Before I used to use my trusty finger. Hoping B+ doesn't get me.
I had a laughed watching Vice Grip Garage. When he connects a battery to a car he's resurrecting, he sniffs around and looks for smoke.