Wire #10 is connected to the neutral end of the T-2 winding set. This is the neutral point of the generator when connected in a 3 phase wye configuration. There are three different configurations shown on this page. Best to figure out which configuration you have. The lower left and right diagram both #2 and #10 are connected to T-0, neutral. The upper right diagram #2 is connected to the #9 end of T-3 and #10 is connected to #8 of T-2, both "hot" and out of phase.

The initial problem seems to be a lack of excitation. The usual cause of this problem with machines that have set idle for any period of time is slight oxidation on the voltage adjust rheostat. The winding labeled F, or I is the main alternator field and is energized through the slip rings on the main alternator rotor. The exciter field is energized through the path through the adjustable and fixed resistors.

If the machine was working when shutdown last then it would be reasonable to figure that it was wired correctly.

I agree, move the connections at your own risk. Never know what someone might have figured out in the past to "get er done".

In any event, the regulator system has to have some kind of voltage reference to regulate from. 2 connections to the neutral won't do it.

Maybe the wires connected to the neutral/ground are T10 (large wire) and 2 (regulator feed wire- smaller) and there is an additonal regulator wire (10) connected to T8.

Take a look at the generic left hand diagram. There are "sensing" windings associated with the output from the T-2 winding pair. The main windings may be connected in either series or parallel, depending on the desired output voltage. The good news is the regulator circuit usually either works or is obviously burned up. These are generic, basic diagrams and several critical parts are not shown. Probably done to save ink or clarity.

The basic excitation, if working, will produce an unregulated output. A DC voltage measurement, while operating, from #5 to #F2 would be informative. These point numbers are shown on the left hand diagram.

It would help to know what configuration it is.

Based on the one comment from the original poster that #2 and #10 were connected to the neutral, it should be the more common configuration.

Until the exciter field is energized the regulating circuitry is out of the picture.

The exciter field voltage reading would be a good first step.

It is also a good idea to keep in mind that these generators do not have a ground ( zero volts) point unless you make the external connection to a common ground reference.