Thank you sir! That is exactly the info I was looking for. I didn't think to check the installation sheet. Ordering one tonight. 

So I have the basic non-sound equipped large scale Thomas.  I want to add the Bachmann DCC Sound module, but I also want to have DCC control of the engine as well.  Is this board just the sound, or do I need to add another chip as well?

Could it be the pick-up shoes not making good contact with the wheels?  Maybe take it apart and clean the contacts on the streetcar itself.

I had a similar issue.  It turns out I had the reversing track reversed.  The Trolley would only travel in one direction, hit the end section and just stop.  The light might be voltage supply issue?  The plug might fit, but is it the same supply voltage?  I can check when I'm home tonight and see what the wall XF is rated at if you'd like.

Well, the #148 worked OK.  It still pulls a bit thru the "S".  Per Len's advice I went ahead and added a 3" straight between the switch and the curve.  That fixed the problem without having to replace all the 5's I just installed! I think I am going to try and find some Kadee #146's, which have a little bit longer shank(??) than the 148.  Just to try them out and see if that works. 

So I did a search and came close, but not quite to the answer of my question.  So here goes.
I have the Bachmann North Pole and Southern passenger car set.  Actually 2 sets.  I've had them at least 10 years, and the couplers have finally gotten to the point of needing replacement.  The local Hobby store recommended the #5 as being the standard, most common coupler.  Much nicer...should have done this 5 years ago.  Except...when I shunted the train into the siding and bam...multiple derailments, cars tipped over...and my son informing me "Daddy...bash!"  That's when I discovered the radius clearance doesn't work as well as the replaced whisker type coupler.   
Some searching here leads me to think I need to ask for the #148.  The clearance I'm looking for is essentially two 18" radius curves in a "S".  Does the #148 have a wider swing clearance? (Not sure of the terminology here, sorry!)