If it's only one seat malfunctioning and only on the "high" setting, it may be bad thermostats (there are 2 located at the base of each seatback). If it's only one but it acts up on both settings, the switch is a good bet. If they're both malfunctioning on all settings, the problem will be in either the heated seat relay, which supplies power to both, or the ground, which is common to both seats on the G35. The ground lug is on the left front floor and sometimes they'll corrode, carrying enough juice to light the indicators and run the seat motors but not enough to make the heater elements hot. On the 12V side, the relay contacts carry a lot of juice and can get crappy with old age. To check, you should see constant rail (battery) voltage when measuring from the heater power pin under the seat to a good ground. If so, the 12V side is good. With the heater on high, the ground pin should read no more than about 0.05V. If it's higher, then the ground connection is crappy. Of course you might also find corroded or burnt pins in the seat connector, that's common but not likely if it's both seats malfunctioning. Try to make your measurements while the seat is acting up, things like worn relay contacts often need to heat up before they'll act up. Hope this helps you.