Does anybody know how to connect the chuff-sensors to a Phoenix sound board?

I'm in the process of converting my Heisler to radio control using a Crest receiver/controller/sound unit.  When I run for more than a few seconds it registers an overload- something that has never happened on my other locos (including a 3 truck Shay which, with 3 motors, should draw more current)
I dismounted both trucks and tested the resistance of the drive circuits including motors: They register 7 and 8.5 ohms respectively (which at a typical running voltage of 10v would draw 1.1 and 1.7 amps respectively). I presume that they should both be he same, but 2.8 amps seems a high current drain and explains the overload.  Does anybody know what the resistance/current drain should be, and what I can do to get it down to an acceptable level?  My first thought is problems in the motors, but replacements are not available on the parts list on Bachmann's site.  I'm based in the UK but Bachmann Europe have no stock either.  All suggestions welcome!

I have aquired a second hand Heisler with lots of wires detached from the pcb : Does anyone have a service sheet with a wiring diagram? I want to convert it to r/c battery so I guess it will be the DC diagram I need.  Also, does anyone know how to dismantle the front truck for service?  
My usual source of such information, the bachmanntrains.com website, is strangely lacking in Heisler diagrams but they must exist somewhere!