You don't need to do anything with the ID
button for it to fly the ILS. Unless you are a super geek, don't even use it. In the real world it is meant to correctly identify the station you are listening to. You might listen to it once to confirm the correct station and then turn it off, if you even listen to it at all.
FTRGUY's Basic Steps to fly an ILS.
1. Get the Frequency and Course from the Map page (not GPS map).
2. Put the Frequency in the NAV 1 and the Course in the CRS box in the autopilot controls. (The course just helps me to orient myself better. I also put it in NAV 2 just for kicks)
3. Turn Autopilot ON
4. Make sure NAV is selected and not GPS.
5. Make sure APP is selected.
6. When glideslope and localizer are intercepted, the Autopilot will fly it almost to touchdown.
FTRGUY's Advanced Steps to fly an ILS
1. Do all of the above except #6.
2. A good pilot will know where he is at all times. If you can't figure it out with the GPS and the MAP page, stop here and don't worry about reading the rest.
3. Draw an imaginary centerline that extends from your intended landing runway about 20 miles. (This is done in your head)
4. Position yourself so that you intersect that extended centerline by about 30 degrees off. Example. If your final runway heading is 090, fly 120 if coming from the northwest or 060 if coming from the southwest. Try to be on the localizer no later than 10 miles.
4. Set this Heading using the HDG function on the autopilot.
5. Altitude-Try to be 2000ft AGL (Above Ground Level) no later than 8 miles out. You should intersect the glideslope somewhere between 8 and 6.5 miles, depending on actual height above ground. Once again use the autopilot and set the appropriate altitude in the ALT box and make sure it is selected.
6. When the autopilot starts tracking either glideslope or localizer, the ALT light or the HDG light will go out on the autopilot. If they are still on, the autopilot is not flying that portion of the ILS.
This is meant as a general approach and works just about anywhere. If you intercept the glideslope with too much of an angle, the autopilot will swerve all the way down and never line you up properly. It just can't handle big angles unless you are way far out.
As far as altitude goes you can intercept it anywhere. There is a general rule in aviation that with a 3 degree glideslope (which most are), you lose 300 ft per mile. So at 5 miles, you will intercept the glideslope at 1500ft or so. 6 miles 1800ft. This is also a general rule when shooting a Visual Approach when there are no glideslope indications.
Hope this helps,
Naval Aviator and Flightsim Guru