I had another instrument lesson tonight right after work (working on my instrument rating). I am finding that the transition from "work thinking" to aviation takes a little while and going from one directly to the other is not a quick one some days. This time my instructor had me flying the LOC 27 into KSAN (San Diego). This is the first time that I had seen that approach and my first lesson was that while I set up and briefed it correctly I was not really ready to fly all aspects of it. I was told to fly to POGGI and hold sound on the 180 radial. It was a no wind situation so it was not too difficult but could definitely have been better. Then I got vectors to VYDDA and stabilized onto the approach course without any trouble and everything was going just fine. And then he hit me with an AHRS failure and it went downhill for a while. I navigated by compass reasonably well but was directed by the tower to take the published missed approach (MAP) was short of the MAP and while climbing to 2,550 set up NAV-2 to get to MZB. That went ok but I started the turn to the MZB R-255 before I had gotten to the MAP. Another experience was fumbling with the GPS when I did not really need to. My previous couple of lessons were GPS approaches so I was mostly doing it out of habit. As usual, I learn more from the mistakes and tonight was definitely a learning experience.