I have a 38 ton, two truck shay. (1:20.3)  Added new style trucks after two years running, goes better than ever.  (Love the shay and the climax!)
I used a simple 'chuffer' sound circuit for years which reacted to track voltage.  I have tried upgrading to a unit which is activated by the Shay piston activated switches, but no luck.  I get a permanent closed circuit on the board.  I loosened the two screws beside the cylinders and it works intermittently, but I cannot get it to work properly.  Any ideas would be appreciated. 
Are there quality sound boards which work off track voltage, or do I go back to the 'chuffer'?