Model Railway Forum

Have a look online at Chadwick model railway loads of help from Charlie Bishop .

Hopefully you have used two different insulation colures of wire for the droppers and the same colours for the Bus pair of wires. e.g. Red and Black etc.

You need to check all, and in my example of red and black insulations, that all the red droppers connect to red bus wire. Then on top of the layout ensure all red droppers connect to the same sides rails, i.e. all red to the outer rails everywhere.
The cause will almost certainly be one or more droppers connected the wrong way around to either the rails to the bus pair.

Time spent looking carefully at the wiring will reveal the problem.

I cannot speak highly enough of Chadwick Model Railway and Charlie Bishop - he makes everything very very clear.