Twin coil switch machines will burn out if the power is applied to them for longer than the momentary contact needed to make them switch. I model in ho, so I don't know much about n-scale, but I suspect Bachmann uses the same design in both scales. I think you should have 3 terminals on each switch machine. One terminal will be common, and the other two will be for moving the points right & left. You can check the coils with a volt-ohm meter on the ohm scale. Connect or touch one lead to the common terminal. Touch the other lead to each of the other terminals. You should get continuity with a slight resistance between the common and each of the other terminals. If either of the other terminals is open or infinity to the common terminal that coil is burned out. The common terminal is usually in the middle, but they should be marked. Common is usually marked with a "c" the other terminals may be marked with an R for right and an L for left. You want ot check your continuity before you waste time looking for other problems. One other thing, a wire may have broken and not burned out, in which case you won't see any external evidence of the failure.