Hi folks,
>
> I'm just at the stage of wiring up the main running lines of The
> Dormouse Line Mk 2, at the moment for controllers we're still using
> two of the small Hornby type that comes with the train set packages. >
> These controllers obviously have a two core lead that actually sends
> power to the rails one side is plain black the other is black with a
> white line. In order to make provision for future
> replacement/expansion and general improvement I need to know which
> of the two is positive and which is negative. I'm presuming that
> it's usual practice to have a common negative and have a selectable
> positive for block working etc.
>
> No testing equipment (my old mini Avometer died a couple of years
> ago) and I can't find the instructions that came with the sets.
>
> If anyone can send a quick reply I'd really appreciate it - as we
> speak my soldering iron is burning a hole in the table. :-)
The actual polarity of the track feed wires changes when you reverse direction with the controller. The mark on one wire is only to assist in identification. You should be OK if you connect the common return wire to the same terminal on each controller and to the same rail (left or right). You can connect wires from the other terminal to isolated blocks of the other rail. This works as long as the controllers are powered from separate transformers. Common-return wiring is not suitable if you have a reversing loop or triangle on your layout.
You should be able to buy an analogue multimeter for £5-10.