AVR with bridge?

here are other photos that may help.

I second that.  The brush assembly is a giveaway, as is the printed message about adjusting "pot 2 on the regulator board" and the picture of a circuit board covered with integrated circuits next to a cluster of three small transformers (probably the step-down transformers to power the circuit board and provide it with a stepped-down sample of the voltage).

All that stuff about self-exciting generators doesn't apply.  This one has a voltage regulator powered by and sampling the output and providing an excitation current to the rotor through the brushes.

If you have 30v then you will gain nothing by flashing it.

I'll second that.  30v indicates there's enough residual magnetization to get it started.

I agree with blasting things clean, too.

Afterward you might try making a small adjustment to "pot 2" and see if the output voltage follows along.  That's probably the output voltage adjustment, or a control related to the voltage input level.  The warning is probably because it interacts with the winding configuration such that a change in configuration might cause the unit to overvoltage and burn out the electronics if it isn't re-tweaked before spinning - and to avoid people frying the machine they tell you to turn it to a safe setting when changing config, then bring it up once you're spinning, according to the manual's instructions (which may have more details on how to do this safely and correctly).

You should try to get hold of the manual if you can, before fooling around with it.  Contact the manufacturer for them.  They'll probably be helpful, and the manual is likey to cost much less than fixig something you break by tweakig without it.

If you have changed the bridge, try it for a few seconds without the red transient suppressor (round thing) in case that has gone faulty.

Try the advice about cleaning the AVR board, even using a solvent such as isopropyl alcohol if necessary as you may have short circuit paths across the sensing circuit.

The place to look at is where the the ac sensing voltage ( likely from 1 line) comes into the AVR board. A shorted top end resistor will cause the AVR to think the machine is at rated volts.

Failing that it will likely be an expensive AVR replacement.

This might be a lead for you to try, they supposedly have a lead on this series in pdf format.

Underground Lightning Rod, I know the unit has been sitting without use for 8 years and suspect it was purchased at an auction since it has a Texas Highway Dept. asset tag on the panel. The folks I got it from had their machine shop crew get the engine running, but it wouldn't produce electricity. They said everyone they talked to about repairing the unit "ran backwards" because it looked to complicated.

Then the genny may have been dead when they sold it - and the reason it went on the block.

Not a killer by a long shot.

Even if the electronics are shot and an unfixable mystery black box, if the genny proper is OK we can probably come up with something.  (Start by unhooking the brushes and outputs from the circuit board, feeding the brushes a variable DC current and watching the AC output of the phases.  Then you'll have a reading on the rotating machine's condition and its excitation current vs. open-circuit voltage, which will get you off the ground for designing a new controller.  Then check out how the transformers, meters, bridge/whatever block, and any other off-the-regulator-board stuff is hooked up, and we can look into whether it might be in condition for reuse and simplification of whatever we come up with for the voltage control.)

Also, if the unit is so old the dox are lost in the mists of time it is likely the components are well-documented and the board could be reverse-engineered pretty trivially, followed by a straightforward diagnosis and fix.

Provided you didn't wash the markings off with the alcohol.  B-(