I'm trying to install a new Honeywell RTH6500 thermostat on an old heat pump system that has regular plus emergency heat and the closest matching diagram says to put both the white "W2" wire and black "E" wire into the same port called Aux/E. (pic attached of instructions page)

1.) Is this right?
2.) Can regular and EM heat work off of the same port? (W2 & E wires in same port)
3.) I get all the other wiring matchups (I think) but what am I missing?

Here is what I have on my old system: (Some of the labels could be wrong here)(pic attached with wires still installed on a regular Hunter Thermostat)

G = Green wire
C = Blue wire
O = Orange wire
W2 = White wire
E = Black wire
R = Red wire
Y1 = Yellow wire

The New Honeywell RTH6500 has two wiring rows for Conventional or Heat Pump: (pic attached)
Top Row - Conventional: K__Y2__W2__G__W__C__Y__R/Rc
Bottom Row - Heat Pump: K__L__AUX/E__G__O/B__C__Y__R/Rc

What goes where? W2/White and E/Black are mysterious.

G to G on RTH6500 = Green wire
C to C on RTH6500 = Blue wire
O to O/B on RTH6500 = Orange wire
W2 to W2??? on RTH6500 = White wire
E to ??? on RTH6500 = Black wire
R to R/Rc on RTH6500 = Red wire
Y1 to Y?? on RTH6500 = Yellow wire

Thank you very much for your help!

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  • Can you show us a wiring diagram or photo of the wiring at the furnace/air handler end of this setup? That's going to be the key in figuring out why W2 and E are on separate wires in your setup. (Also, is your aux/emergency heat electric, gas, or...?) – ThreePhaseEel Jan 3 '18 at 2:31
  • Thanks for the quick reply. I can get a pic of the air handler unit in the attic tomorrow (it's night and freezing up there right now). I know it is a 2 year old system and has electric emergency heat. The previous thermostat before the existing Hunter was a very old Honeywell unit from 1992 which is where I got all the wiring names/tags from originally. Again, the W2/E etc. tags may be wrong. – Scott S Jan 3 '18 at 2:36
  • I couldn't find an easy access to all the wires inside. I did find a wiring diagram on the outside posted here: imgur.com/a/hQMxJ Does this help? – Scott S Jan 3 '18 at 22:38
  • Is there another wiring diagram label on the unit? Or is there a make and model number you can provide for that matter? – ThreePhaseEel Jan 3 '18 at 23:40
  • I didn't see one. I'd have to take off the whole front panel to get at the wiring inside hopefully. Can try again tomorrow afternoon. – Scott S Jan 3 '18 at 23:53

It looks like y1 on old one is Rc on the new one,unsure of this so satisfy yourself before trying connection based on this observation.Also have you noticed the link between R and Rc,I would question this.Try asking manufacturer of after market part for advice.STeve uk Engineer.The instuctions are poor and the terminal markings maybe wrong.with thermostat.com are mentioned for help.Sorry I do not understand the istructions.I will sleep on it. Had another look,Must say may not be compatible. Honeywell surprise me,Action to take,do not know.I have not given up,but hold little hope for success.I am now checking my suggested connections before posting them.good question,too many combinations.Einstein had it easier. Respect STeve uk.L?Wire missing. Steve has been called many things,genius is not one of them.Steve uk.You are missing,Internal diagrams for the controller,and external diagrams for equipment to be connected to it,also cable overal diagrams. All factors to carry out this project. I have touched on subjects relating to this before and now have little to add.pn,System may have lv electronic control as well,consider this.Do not mix wiring.All parts of the system may need to be wifi compatible to use wifi controller.

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