@plasmaniac : Whatever you're trying to achieve: with that little and useless information you're not going to get useful feedback. The thickness of the wire has nothing to do with the output voltage of a (auto or not) transformer under no load. With load, the limited thickness of the wire creates resistance which will reduce the output voltage. You have not given any value for the expected load
Wrapping a straight wire with another wire does not create a transformer. What we understand when we read wire is typically a copper wire which, being not magnetic, does not lend itself to the construction of a transformer's core. A transformer's core needs to be magnetic to concentrate the magnetic flux.
As
@BobK stated: No transformer will generate an output from a DC input.
