Well, no replies, so I went back to the drawing board...and solved the problem!
I can see how this could happen a lot with crossovers, so maybe it is old news to you guys but it sure was not initially to me...hope this can help somebody else new in model rairoading...
I did find what the problem was! no faulty wiring, but faulty crossover. I looked at each rail separately, everything was fine, so the only place where "current" could cross was at the frogs on the faulty crossover. The frogs are metal (they can be powered for short base locomotives), and there is supposed to be a very little gap between the frog and the rails which technically insulates the rails from the 2 different polarities where they meet...well, one of the rails was touching the frog effectively connecting two rails of different polarities when the train comes and fills the gap on the other side of the frog....
anyways, it was an easy fix, just reinstated a small gap and now the trains can go through without creating a short...
I can see how this could happen a lot with crossovers, so maybe it is old news to you guys but it sure was not initially to me...hope this can help somebody else new in model rairoading...
I did find what the problem was! no faulty wiring, but faulty crossover. I looked at each rail separately, everything was fine, so the only place where "current" could cross was at the frogs on the faulty crossover. The frogs are metal (they can be powered for short base locomotives), and there is supposed to be a very little gap between the frog and the rails which technically insulates the rails from the 2 different polarities where they meet...well, one of the rails was touching the frog effectively connecting two rails of different polarities when the train comes and fills the gap on the other side of the frog....
anyways, it was an easy fix, just reinstated a small gap and now the trains can go through without creating a short...