Checking phasing with the test light

One of the most important requirements of a multi-block layout is that the phasing (or polarity) is correct. Trains will short at block boundaries if this is not correct. In a multiple booster configuration, it is essential that each booster's output properly matches up with the adjacent blocks. Use of a test light can ensure this is the case.

The test light leads do not have to be connected to one booster for the light to work. This means the light will work across booster boundaries, which will be the basis of checking for proper phasing.

To check for proper phasing, connect the light across the rails in the same block. The light should light. Next, move one connection over to the other side of the gap to the same rail. Again, the light should light. If the light does not light, move the connection over to the other rail. If the light lights, that means the phasing is incorrect and the wires will need to be swapped.