Could you explain how/where you added the contacts?

I have both the earlier version (which has the couplers mounted to the trucks) and the later version (body mount couplers).

Neither of mine run very well.   The later version especially is quite noisy.   I don't know if I just got unlucky or if this is characteristic of the model.   

Also, converting to knuckle couplers with the new version presents a slight problem because the front of the loco has a "plow" attachment which interferes with the coupler.  You'll either need a long shank coupler to make it work or need to remove the draft gear box and move it forward.   It wasn't an issue with the rear coupler, however.