That's exactly what it was.

It took upgrading to a CW-80 transformer to figure out what was going on. The old classic 40W transformer didn't have enough output to make marks on the track.

Once I had marks on the track it was a simple fix: The locomotives were shorting out on the point of the frog rail. Strategic pieces of black duct tape cured the problem.

I added two brand new switches to my layout, Lionel 5021 manual switches, to make a turnaround.

Every time the engine goes over one of the new switches, it shorts out and trips the breaker in the transformer.

Once the engine is pushed off the switch, it operates just fine. It has no problems on any of the old switches on the track, which are just older 5021's and 5022's. Just the new ones.

Any ideas? I can't really see anything different about the new switches.