I'd start by looking for a polarity problem between the 2 track directions. You may have to gap the entire crossover (4 double-rail gaps) to separate it from the section with the other polarity of power. The loco may be bridging something it shouldn't. Only 1 loco or 1 loco type/maker or the entire fleet? Is this DC, or DCC? DCC is more sensitive to quick shorts between wheel flanges and point rails or at the frogs. DC is slow to complain and by then the offending wheel has passed along. Your NMRA gauge is invaluable here!
Have fun, George.
Hi again. I'm not familiar with those Bachmann Crossovers, but it sounds like the frog is live to the wrong rail. Looking at your photo ( thanks for putting it in, it really helps to visualize), if you think of a loco coming along the topmost track, after setting both point-sets to the crossing-over alignment, you are saying that the first set of wheels to hit the lower frog causes a short. I'll assume that the lower track is in the correct electrical polarity to move the loco to the right if it got there. BTW, does it short the same way if the loco were to come from the lower track, heading for the upper, except this time the shorting is at the upper frog? Notice that the curved rail from the upper track heads toward the lower frog, and vice-versa. The question of the day is where does the frog get its power? Aligning the points should cause the frog to power correctly. I'm wondering if you've set up a reversing section, or if there is something wrong with the crossover- doubtful, as you don't have a short until the wheels get there, and straight-on travel is OK. Where do the tracks go off to the right? And to the left? Do they loop and become each other? If so, you need to put switches on a panel to reverse the track power in that loop.
Fast check: with the switches aligned to enable a crossing, put a loco on each track facing each other but some distance apart so they don't actually go into the crossing. If you turn on the power, they should both move in the same direction. If not, you need to attack this as a reverse-loop problem. There are a lot of threads in these forums about reverse loops.
Let me know what you find, I'll keep an eye out for your answer. Somebody out there has likely worked with these crossovers and been in this situation. Maybe they'll join in. Are you near to a knowledgable hobby shop, or someone with a working layout? They should be able to help better than I can from a distance.
Don't give up hope, we'll get to the bottom of this 1 way or other.
George
I suspect you may not have connected up the wiring to the tracks correctly, apparently one set of tracks has the + and - reverse of the other. The crossover has gaps in the rail already, so you can run on either straight line with no problem, but when you try to use the crossover, the wheels of the engine are connecting the gap between the + on one rail and the - on the other causing a short.
If you reverse one of the tracks wiring, so both sets of track have + on say the right rails and - on the left, you should be able to go thru the crossover with no trouble.
Try this - take the leads to one of the two straightaways and reverse them, then try running thru the crossover.
Don't remove those wires from the frogs!! If they are what I suspect, they are for you to purposely power the frogs by means of a relay or sw motor contact if you need to. Some mfgr connect the frog to the point rails to get the power from the selected track. This works OK if you keep the contact area clean. But if you slack off like me, the contact area gets crud on it and the locos, especially short ones, will have a pwr shortage there and stall. On all my turnouts, (most of mine are Peco, with some from Walthers, Atlas and Shinohara) I solder a wire from the frog area to a relay to ensure good contact no matter what. The relay is flipped by the switch motor. If you don't need the extra wiring, just tape them and put them somewhere below the roadbed.. you never know if they'll be handy in the future!
Still having fun... George