Jim Jansen says:

I assume you are talking about wiring
to the track on the turntable bridge.
Wire the switch crossing as described above.
Wire the two wires from system track to the switch and the wires from the switch to the bridge.

Sheldon Clark says:

It is possible to obtain the same effect automatically by taking the bridge track pickup from metal tags, one at opposite ends of the opposing rails – if the bridge is transverse (cross-wise) to the position from which you look at it, one contact is at the right-hand end (say) of the nearer rail and the other is at the left-hand end of the far rail. They each should be made to brush against a rail bent into very nearly a semi-circle that fits into the turntable (T/T) well – just like the real thing, in many cases. In other cases, the weight of the bridge is taken by the central bearing, but it is immaterial whether this is the case with the kind of real T/T yours is modelled on – you can still rig up this kind of collection system. If you feel that rails would be unprototypical, because of the original design of your T/T, you can gain the same effect by attaching two pieces of copper, each again bent into (almost) a semi-circle, to the inside of the rim of the T/T. Whether you use rails or strips, there must be a gap between them at each end, to avoid shorts this gap must be less than the distance between where the moving contacts touch the supply rail/strip, so that you can be assured of proper contact at all positions of the T/T. There will be an interruption of current supply to your loco as the moving contacts pass over the gaps. This will be unimportant unless you have digital sound, in which case, the smaller the gap, the shorter the interruption. (Maybe on-board capacitors will cover this). In either case, it will probably be necessary to fill the gap with some insulating material, such as styrene strip, curved to the same radius as the supply rail/strip. On balance, though, a switch would be easier – but you have to remember to use it, whereas the system I have described is automatic. It goes without saying (at least, it very nearly did) that each of the contact strips/rails must be supplied with power at opposite polarities.