[Russ Beavis]

My vote's with Alan on this one. Please confirm that, when powered up, all 3 power LEDS are fully lit on the Digital Sidecar (all 3 LEDs next to the power input). If you're not providing 12V from the PD (typically due to clamped insulation at the PD's WAGOs per Alan's comments), the 5V power LED will be dimly lit (due to phantom power from the 37-pin cable) but the 6V and 12V LEDs will be VERY dimly lit or off.

If you've got a chassis isolation issue (you should check that too), you may have found a new path for phantom power. If all 3 power LEDs on the Digital Sidecar are lit, remove the breaker in the PD that provides DSC power and see whether the power LEDs are still lit. If so, you're sneaking power into the DSC via some other path (maybe a combination of 37-pin cable and chassis isolation). If the LEDs do turn off when you remove the breaker, you may still have a chassis isolation issue but it's hard for me to imagine how that current path could be closed. You might need to start disconnecting digital I/O devices and Spikes, Vics, Jags to find the culprit.

Russ