If you are reading any AC with the bike not running....get a new meter! There shouldn't be any kind of fluctuating voltage that it's measuring so it's likely any actual AC voltages you might measure are possibly giving you an incorrect measurement. You can't trust it to be accurate. Borrow someones quality meter and see what it reads. Sometimes a traditional analog meter is better than an imprecise (and inexpensive) digital meter for complex waveforms and not a true sine wave. If you shop for meters, a "TRUE RMS" ability is desired.
(I spent most of my working career as an electronics tech.)

Lots of meters when set to AC are designed for 60 hertz and they use a special circuit to convert the sine wave to a fixed number.
They're very sensitive to very slight voltages and even placing your finger on the positive probe can give a false reading from residual AC on your body. With the bike shut off "for sure" there is no AC being generated, but the bike and it's wiring are acting like an antenna giving a false reading mostly from closeby house wiring.

For a demo, set your meter on a sensitive AC position (say 5 vac) and touch only the positive probe tip. The reading will vary depending on your closeness to active wiring. The only time an AC meter is accurate is when it's properley connected to a 60hertz AC source.

Glad you got your problem on the run...

patuca

all very good information here, thank you everyone