Decoder Install in older Spectrumn

[Rusty Rail]

I have a matched set of Spectrumn F 7A-B units that I assume are older, but new in the box unopened. I want to convert them to DCC and I am using a Soundtraxx decoder function only, no sound. Can you tell me if the copper tab on the bottom of the motor needs to be removed? And is this where I should attach the decoder ground wire? When I took the engine apart, I found the red (+) wire and the negative (-) soldered to the top of the engine, seemingly on the same post. I have two pictures for you, but I can't send them. Seems the files are to big.
The motor in these have brass flywheels on them, so I guess they are a newer design? Thank for your help. And let me know if there is another way to send pictures to you. Thank You.

Rusty Rail