Jerry,
Your symptoms are somewhat intermittent and could be related to heavy current draw by the PTO when it comes up to working temperature -- sometimes the early indications of internal winding shorts would be evident only when hot. The resistance you measured at room temperature is well within nominal, but it could be that the PTO has a lower resistance due to an internal short at elevated temperatures. A PTO may still engage properly and stay engaged even with some coils shorted, as it would then draw higher current. Electromagnetic coil strength is stated in terms of ampere-turns...
When the light on the dash comes on, you say that turning off the PTO immediately clears that condition -- if you turn on the headlights does it come back on? Remember that for the original Onan engine, the dash light is a VOLTAGE indication and not a charge state indication:
This means that the battery age and condition, the connections and grounds, the voltage regulator and the loads (headlights, PTO...) may all individually or in combination be involved in the dash light coming on. I am less familiar with the charging system on the Vanguard -- or even if that uses the same voltage indication or is a true charge current sensing method... Perhaps another member here with that re-power can chime in with some more specific advice. You could of course measure the battery voltage when the light is on and again when it is off -- that would tell us something. If you have schematics you can post to this thread that may help also.
Chuck
...another thing to think about in a re-power situation is the mechanical mounting of the PTO assembly itself -- sometimes the spacing is such that the moving part of the PTO clutch can rub lightly on the stationary winding face. If that happens, then the insulation/potting can wear thin and the coils become shorted. Probably not the case here, but thought it should be mentioned...
