The most reliable way to add switch position feedback is by using the extra set of switch contacts on the tortoise machines and wiring them to an AUI. The AIU is a cab bus device which will report the actual status of any device that can complete a circuit and short an AIU input to ground.
Read this: https://ncedcc.zendesk.com/hc/en-us/articles/200933435-Auxilliary-Input-Unit-AIU-
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