I'm installing new thermostat - all wires/lettering corresponds from old to new with the exception of new one has a slot for "w"but I have two wires left "w1" and "w2". "W1" is tan and "w2" is yellow. Thanks for the help!

Do you have a heat pump? Or gas heat?

Neither - both ac and heat are electric - house built in 70's

OK do you still have the package your new stat came in? If so tell me what it says, like does it say 2 heat 2 cool or single stage heat plus cool.

You may need to get a 2 heat t-stat, or put both wires on w

It's model rth600d - which is not on honeywell wesite for some reason - it says compatible with heating and cooling systems - not compatible with electric baseboard heat or heat pumps - doesn't exactly state what you are asking. New one has slots for 4 wires - I have 5 wires.

OK tell me what colors you have, and where you have put them..

Green - g: red - r: blue - y

Does your outdoor unit run during heating and cooling or just cooling?

Just cooling

OK if it runs in just cooling then you have 2 options. You can take the t-stat back and get one for 2 heat. Or you can keep that one and put both wires under the w terminal. Your old t-stat was wired so that your heat would come on in stages

Fyi - it's a rth 6400d not 600 - I typed it wrong - sorry!

Thank you so much! I'll let you know if this soccer mom did it!

So far so good - nothing exploded nor caught fire - ha!ha! Thanks again!