Help! Upgrading from Trane to Nest. Not sure what the “+”, “-“, and S” wires refer to

[Barnacle570]

Any body know what the +, -, and S wires refer to on a trane thermostat wiring?

[Patrick_Caezza · Accepted solution]

@Barnacle570 

The terminals marked S+ and S- are for external sensors which none of the Nest thermostats support. You can just tape them off.

Sometimes you might see an L terminal which is used for a light on the thermostat. It too can be taped off.

The B terminal on most Trane thermostats is the C terminal.

[Barnacle570]

Oh man thank you so much!  That’s really helpful. One other question. If I have a positive terminal, a negative terminal, and an S terminal I assume all 3 of those are for sensors right?  Also, I assume these are probably temperature sensors?

[Patrick_Caezza]

@Barnacle570 

Corrrect