How do I test to determine if the motor in my Doodlebug is isolated from the frame so I can install a DCC decoder?

2 Oct 14 1817 hours Sierra
  I failed to mention that the unit is N scale that I acquired when my brother-in-law passed away one year ago. I don't remember when he purchased the bug but think within the last five years. I can see no evidence of motor isolation. If it is not isolated, will a piece of electrical tape underneath the motor suffice?