Thinking of buying an MTH engine,what to eatch out for?

The engine your talking about was cataloged in 2005.  It should be the 3v system.  I believe this new old stock is no longer under warranty by MTH.  However, if the shop is a service station perhaps you could come to an agreement where he/she will warranty the product.  The battery should not be an issue. I've never had a 3v system that had issues out of the box.. and I've bought a lot of old new stock SG tinplate. The b unit is non powered.  The tether is simply there to connect power the lead a unit to the trailing a unit if you want an aba set up. 

Sunrise

Have the dealer replace the battery with a new one. One that has been sitting uncharged for nine years is not going to be much good.

Pete

Frank - You should request that the retailer run the locomotive on their test track.  If the loco has been sitting for 6 years the battery will probably need recharging. Ask the retailer to do this for you or give you a charged battery ( a BCR is your better bet ).  If the retailer is using DCS they can put your loco through all the command modes and demonstrate them to you.  These modes would be voice announcement, crew talk, couple and uncouple, horn and bell, head lights off / on etc.  

The battery provides sound when there is no electricity to the rail ... those 1 or 2 second power interupts when you are changing direction of the loco via command mode.

A fully charged battery will last ( provide sound ) 6 to 8 seconds after track power is shut down.   If track power is shut down and the sound immediately goes out the battery needs to recharged.  

You might want to check with MTH regarding waranty.  I would think that since your loco is brand new it would be under full waranty ..... but MTH did make some changes to their waranty policy ( how many years from date of manufacture the warranty will cover?)  a few years ago.... so check with them first before you purchase.

As of the tethers on the B unit .... they are there so the non powered A unit can have coupler function when in ABA lashup.  You connect the tethers just below the couplers on the A units.

My experience with MTH products has always been excellent.... but I have never bought a locomotive that had been on the shelf for 6 years either.   I have purchased MTH locos used and brand new .... all to my utmost satisfaction.

I think that might answer all your questions.  Again though check with MTH directly regarding the warranty BEFORE you purchase.

Good luck.

Patrick 

Whoops!  Paragraph two of my prior post to you should have said running in "conventional mode" instead of command mode.