Ancient thermostat wiring help - T and X2 wires among other things

[NotBigTex]

Hey all, 

Have an old American Standard system (TWE048P130A0). 

Wires used on the wall thermostat are:

T

X2

R

O

G

Y

B

W

Would appreciate help determining what goes where, and what should be ignored. Couldn't find instructions on a wiring layout like what I have on my thermostat. 

Hoping one of these wires functions as a common, so I don't have to worry about charging as well.

Thank you all for your help! 

[NotBigTex]

Here is a Pic of thr current wiring

https://flic.kr/ps/3obQCa

[Jenelyn_O]

Hi NotBigTex,

Thanks for posting in the Google Nest Community forum. It looks like you have a heat pump system. Your system is more compatible with the Nest Learning Thermostat. Since you have the Nest Thermostat 2020, and it has only six terminals, we may disregard your existing 2 wires, which are your Emergency Heat (X2) and your heat anticipation (T). Also, connect the orange wire from O to *OB on the Nest Thermostat. 

Let me know how it goes. 

Best,

Jenelyn