Not understanding how you use jumpers to emulate an OFF condition when OFF has no connections.

IF you are using an extremely low range on your meter, you may simply be measuring RF in the air. IF you have "jumpers" dangling off the ends of your test leads, you have a bigger antenna.

Bill, thanks for the input. Yes, emulating the OFF condition is really just jumpering C and G to allow the thing to start. PTO on = no jumper at C and G, jumper from B to E and jumper from A to D.

I get what you are saying about the RF, but the meter is set at 20VDC. Shouldn't be sensitive enough to be picking up over half a volt RF unless I'm about to get hit by a meteorite ;)

Try connecting some kind of an electrical load (a common 12 V test light bulb) in series with your jumpering set up where you have been detecting the .57 to .6 VDC.
It is actually pretty typical to pick up some stray "ghost voltage" in automotive wiring. Even the so called "dielectric grease" the switch OEM uses when assembling the switch might conduct enough milli-amps of current to register that small amount of voltage on a VOLT METER but still be unable to accomplish any "meaningful work" when a real load is applied to the circuit.
The point of the light bulb is to offer a resistance load into the circuit to "absorb" the stray or induced voltage (if that is what is present) instead of it going unimpeded into the volt meter.
Adding an electrical light to the circuit often makes the ghost reading disappear.
To offer a couple of real life examples from my own experience, I have had many cases where ghost voltage would show up on a volt meter in an unloaded circuit, only to go away when a very small load was added.
I have also experienced cases where test results using a volt meter indicated a switch was good, but yet the circuit would not even light up a DC test light.
The upshot of that is that the defective switch would still conduct 12 volts that the sensitive meter would show, and that might make you believe the switch and circuit were good, but the defective switch was incapable of carrying even the miniscule amperage required to operate the 12VDC test lamp bulb.
If you have a 12VDC test light, connect that in series with your volt meter and see if its slight load makes the ghost voltage go away.

This post was edited by mownie on Sat, Aug 2, 14 at 9:14

Mownie,
Sorry I didn't respond sooner, thanks for the info. Going to try your suggestion tonight. Makes perfect sense, hopefully I've been freaking out about nothing this whole time....

Yep, that did it! putting a test light across dropped that voltage right to zero, and nothing was visible on the test light. Put it all back together and life is good. Thanks for the insight!