is there a downside to doing this?

Creating a common ground between MRC and V will allow you to use the outer track rail works just fine. However, be aware of one possible cause of a short ---- some Lionel accessories use their metal base/frame to get power to the accessories' working part. If you connect the Power lead from the V to the contact that uses the metal base/frame, the a short would occur if the metal base were to accidentally contact the outer rail. Alleviate this possibility by making sure you connect the ground to the accessory's metal base/frame.

Example of a Lionel accessory that used the metal base/frame to transfer power is the #494 beacon. Below is a pic of the connectors.

Also, make sure both transformers are in phase with each other.

thanks for the comments.  I already have the plugs marked on ALL of my trannies so that I know how to plug them in to keep them in phase, so that won't be an issue.

Based on @MED comment and the fact that no negative comments are listed, I'm going to try this on this year's Christmas Layout.

As always, thanks

walt

@walt rapp Looking forward to you seeing your Christmas creation again this year.

Thanks @JD2035RR - I have it all planned out already - track design, scenery, wiring needs, AIU assignments, etc.  Have one or 2 things planned that I've not done before so I'm looking forward to starting on it mid-November.

thanks again for the kind comment

- walt

Best of luck, please share if you can as you start things. We can all learn from your layout!

Mike

Walt,
Be aware that any less than perfect rail joints, i.e. more than 0 resistance, will cause additional voltage drop. Especially when a train is also using that section for power. You may get flickering accessory lights, etc.
Personally, I would run both wires. Also makes troubleshooting easier.

Dave

Gotta' go with Dave here, I think trying to save a little wire here is going to lead to headaches you really don't want.  You're running one wire, just buy some nice 2-conductor copper speaker wire and save yourself some grief.

@gunrunnerjohn posted:

Gotta' go with Dave here, I think trying to save a little wire here is going to lead to headaches you really don't want.  You're running one wire, just buy some nice 2-conductor copper speaker wire and save yourself some grief.

Same here. IME track is a pretty unreliable and trouble-prone conduit for ground *or* power, and I would avoid using it as a universal ground connection unless there's no other option. The potential extra bulk and cost of two-conductor wire is IME trivial compared to the possible interactive effects and troubleshooting nightmares you may be able to avoid by keeping each circuit discrete instead of commingled.

OK you guys made me change my mind. I will not do what I asked

As always, Thanks

@walt rapp posted:

OK you guys made me change my mind. I will not do what I asked

What, was it something we said?

yes