I have a HJ61 12HT sahara and three warning lights have come on: water filter, air filter, and battery warning lights all together. Luckily the instruments have a volt meter gauge and it has dropped from about 14 volts to 10 volts. The alternator was replaced three and a half years ago with a Bosch, and at that time I had no warning lights, just failing battery life. So 29 years from a Denso (one rebuild at 17 years of age) and 3.5 years from a Bosch.