I bought a replacement bunker to use as a tender for my porter, but I can't differentiate the two leads on the light.
I'm used to them being different lengths to indicate positive and negative.
Alternatively, what's a safe voltage to test them with a battery?
I usually put my multimeter in resistance measuring mode (lowest setting) and measure the resistance across it. If you've got the leads the wrong way around, you'll get infinite resistance. If they're the right way, you'll get the LED lighting up and a few ohms of resistance. The current put out by the multimeter is low enough that it won't burn out the LED.