Rebuilt HP 67 battery pack problems

[BobVA]

The card reader motor has a connection to the battery pack via an IC that does not go through the power switch, so there is a path for current to flow to it with the switch off, as seems to be happening for you.

The only possibility I could imagine is that the battery pack has been wired incorrectly, with the polarity reversed, and this is somehow allowing the current make it to the motor through the IC? (I've got no idea what's going on inside that IC, so this is pure speculation.)

I'd definitely check both the voltage and the polarity of that pack before using it again.