push button start and relays

  Let's see if any mad scientist out there can help.  Car info: '02 Mercury Cougar, MTX.  I am putting in a hidden push button start and doing away with the key.  I have 95% of it figured, but I'm not great with electronics.

  I am using a push on/ push off switch.  When it is pushed on, it will bridge the 12v+, accesories, ignition and starter.  What I need is an IC to kill the starter when it sees a tach or coil signal.  I figure one relay to engage when power is intitially applied and a second one with a comparitor that will trip when a tach(or coil) signal of about 8v+ is detected in order to shut off the starter.  Remote starts use the tach signal to stop the starter.  They usually shut off around 600 rpm and I figure that is about 8v+ of the normal 12v+ to 14v+ the coil runs at. 

  Does any one have some made IC design skills?  I probably could figure it out with the IC Op-Amp Cookbook, but alas, I am really damn lazy!  Thanks in advance.

   Why not just use a simple timer to crank the engine. You can adjusted and it will work just like a remote starter without the tach.

  Thought of that one too.  I have been bugging the crap out of a few buddies at the local Ford dealership.  Fixed output times won't account for cold weather and what not.

   Does any know what kind of curcuit or set up a keyless start uses?  I don't know the layout of the gem they use, but that is basically what I am after.

  Thanks for the thought.  There are a BUCH of ways to pull this off with two switches, or just hard wire a keyless start.  I am actually going to us a transponder that will unlock the doors and disarm the starter kill when you are within 10 feet or so.  I am aiming for the system used in the new cady and benz.  I just cann't afford a custom $5000 to $10000 Seimens computer controlled system.

  If anyone can do it, I would love the layout for the circuit in the factory gem or something like it.

  Let me brainstorm tonight and I'll get back to you in the morning.