What's the best way to test the voltage on transformer taps?

[kleptolia]

Hey, it's me again. I am still trying to figure out the transformer thing. My main problem is that I'm cheap and I don't want to pay $40 for a power transformer. I know of a place where I can get surplus transformers for cheap, but it's hard to identify the kind that I need. How can I figure out the voltage of the transformer taps? If I get a transformer that's bigger than I need, is it possible to use only a couple or a few of the taps and tape the rest off? These are things that I want to know before I try it out, because the consequences could be disastrous.
On a random tangent: Isn't it amazing what you can do with electromagnets? One of the least understood forces in our world (electromagnetism) and we have nevertheless made ouselves dependent upon it. Crazy!

[Jazz P Bass]

Unknown transformers.
Unless the transformer has a tag identifying the voltages, the only way is to plug it in.
I would use a Variac & a fuse.
Monitoring the primary current would also be useful.
Now you are down to how much current it can support.
Another unknown.
Unused taps can be taped off.

[kleptolia]

Thank you sir. I'll try that.