My intertherm THERMOSTAT only uses 2 wires i bought a honey well rth6450will it work on only 2 wires

SOURCE: Intertherm to Honeywell thermostat

Typically if you have a yellow wire in the "y" terminal blue is used as common or "c". As far as your jumper from rc to rh, that will depend upon what type of heat you have. If all of your heat and cooling come from your packaged unit outside, yes you will need the jumper. If this does not work maybe you have a bad breaker or transfomer.

SOURCE: Wiring

web is right however normally red is power in goes to r on t-stat white is heat goes to w1 on t-stat blue is common and goes to c on t-stat green if for the blower fan and goes to g on t-stat

SOURCE: Intertherm Thermostat

the wire that is on the x- terminal  on the old tstat will be c-terminal on the new tstat.

SOURCE: Change thermostat

You have caught me without my old books, but I can tell you the orange wire is for the reversing valve on a heat pump. Almost all manufacturers, except for Lennox, are: R=Power (24volts), G=Indoor fan (Blower), Y=Cooling (A/C), and W=Heat. Some t'stat's are set up to use 2 separate transformers (24 volt), that is why you will see Rc, Rh. This is power for cooling and power for heating. If this is what you have, just take the Red wire and strip it back far enough to go under both screw terminals if the unit is a residential one. I've been doing commercial work for over 20 years and have never seen an "A" terminal, so I can't help you there. You may want to double check that. If I'm reading you correctly, I would put the orange wire on the "O" terminal. Don't understand why the "Y" terminal is not used. It turns on the compressor. The "O" goes to the reversing valve to "Tell" the outdoor unit that it is either in the cooling or heating mode.

Good Luck and let me know if I can help any further.

SOURCE: Have a 4 wire input into my thermostat but the

Red wire goes to Rc with a jumper wire to Rh
White wire goes to W
Green wire goes to G
Yellow wire goes to Y