I am replacing an old 24 VAC Heat Pump SECO TA2060 thermostat with a digital Honeywell RTH7500D but the wires do not match.
The wires on the old unit are:
W2 - White Jumpered to E
O - Orange
X - Blue
R - Red
Y - Yellow
G - Green
W3 - Brown ( I believe W3 is used as an
outdoor sensor but I am not100%
sure. Is there a way to check
& confirm this ?? )

The new RTH7500D thermostat has terminals:
RC
R (FACTORY JUMPERRED TO RC)
O/B
Y
G
C
L
E
AUX

Thanks if anyone can help me with the wiring.