Hi Peter,
I think Paul is using an Ice Lite 75 or 50? He showed me at the Nats but I can't remember which one.
The Yellow light flashes when it is collecting data and is on continuously when the memory is full (Not Flashing when it's full). It flashes when it is collecting data. (Normal situation). I don't think the yellow light indicates any error conditions, it only reports on the state of the data logging memory.
If the motor is just oscillating it sounds like you have a failed winding on the motor. So (At least) one of the windings has failed. Simplest way to check is to substitute the motor with another one. (Any cheap brushless motor will do, he does not have to go and buy another OS just to check.
TTFN
John.