MTH 4000 and Lionel RW transformer / common ground

[lionelsoni]

Unless some of your accessories are activated by control rails (insulated outside rails), which includes anti-derailing turnouts like the 022 or 5121 powered from your accessory transformer, there is no need to connect the two transformers.

[capote59]

I am trying to wire my layout using the MTH 4000 transformer for the variable voltage for the track(actually two separate tracks) and a RW Lionel transformer for the constant voltage for the accessories. I am a novice at this. I have read that the two transformers need to be hooked up with a common ground. I have the wires for the layout connected to Track 1 and Track 2 terminals on the MTH 4000 and the accessories(via a terminal block) hooked up to B and D on the RW. My basic questions is this. For the common ground between the two transformers should I connect any of the ground black terminals on the MTH 4000 to the U terminal on the RW? For conveniance, I am using one of the constant voltage black terminals on the MTH 4000 rather than the variable voltage ground for Track 1 and Track2 - I assume that that makes no difference?

Thanks for any help. 

Chris Johnson