Hookup Trane Thermostat to Taco SR504 24VAC?

Newb here, Went to go hookup a new Trane thermostat, and realized my current thermostat was only a two wire. I followed the wire down to the boiler and it’s an easy run so I plan to replace the wire.

It terminates in a Taco SR504-4 box. In the manual it looks like there is a terminal for 24VAC / COM -
Manual here - http://www.taco-hvac.com/uploads/FileLibrary/102-381.pdf

Trane Manual - http://www.nexiahome.com/ProjectDocRepository/TSK400BBX%20IS-a_ENG.pdf

So question is, if I pick up some 18-5 Thermostat wire, make a new run to the taco box, connect the two wires as they are now for the zones, and run a third wire to COM, should I be OK? I’ll combine all the 24VAC (blue wire?) thermostat runs with a wire nut, and run a single wire to the COM terminal. I’ll be using 3 of the 5 wires in the 18-5 thermostat cable.

Everything sound OK? Appreciate it!

You should be able to find 18-3, or 18-4 thermostat wire. A little smaller diameter.
Blue is often used for Common.

You should verify that they are using standard R and W for their thermostats.
Use should measure 24V AC between the 24V common and ALL of the R wires.
When the R is shorted to W (Circuit closed) that Zone should call for heat …
Looks like the LED should come on.

If you are using Zone 4 as priority mode … I would verify this while Zone 4 calls for heat. In this case it disables the other 3 zones … You need to make sure they disabled the (W) wire for those zones and not the (R) wire.

Just wanted to follow up-

I connected everything as described in my original post, and everything is working great!