temperature displays

my existing regulator circuit has only pos/neg output.... I would need to tap into the "in" pin on that circuit connecting it to Q1? you know, it's probably just easier if I buy another 7805 and just build this as it is.... no need to make it more complicated. any suggestions on a relay? or will any relay rated for my purposes do the job?

I was going to use any relay I could find that would work basically... maybe not standard automotive since I was gonna take a look around my dads garage.....he's got tons of stuff like that. a heater would tend to draw a lot of current, so I just need a relay that can handle what the heater would draw, if an automotive relay can do it, I'll buy one. I'm not worried about using smaller components, nothing wrong with overbuilding ;) now about that last comment..... what?!?! if it's easier just to buy a second 7805 I'll go that route, I'm just not sure how to squeeze my existing regulator circuit into this one.

What are you using as a 12 volt source?  

for the heater?? the battery most likely, The heater I was looking at I believe needs to be wired right to the battery. power source for the circuitry components would be any 12v source I can fin in the dash, possibly ignition so the displays/heater will be active with KOEO. just backing up a bit here, you said depending on weather its for heat or cool I should reverse the polarity on the op-amp pins 2 and 3. first of all how would that make difference, what would it do differently, and secondly, I could just wire a switch into that to make it switchable between heat and cool, and go so far as to add some fans for cooling functions? sorry about all the questions, im sure you have better things to do, I'm just trying to nail down all the specifics so I can get this assembled without issue.

The way the picture is, anytime pin 2 goes lower than pin 3 the relay will energize.  From what I am gathering, you need opposite of this.

so I should have the probe connected to pin 3, and the pot connected to pin 2?

correct

I'm still working on the labels, and getting the hang of this program (Circuit Maker 2000) but this is basically the circuit?