There should be 4 fingers, 2 on the top and 2 on the bottom. If the drum appears all black it needs to be cleaned, it should have copper or brass colored sections on it. You can use spray electrical contact cleaner, Radio Shack sells a good one. Or you can use Isopropyl alcohol on a q-tip.
If it sounds like the tender is working and the loco won't run it could be the drum and fingers are dirty and sticking.
Aflyer