Depending on the installation, you could also be experiencing either:
1. An over-voltage "crowbar" where the alternator output is stopped due to an over-voltage event. The crowbar unit may be reset by cycling the switch.
2. With all this hot weather, a voltage regulator overheating event can act the same way.
If it were happening to me, I'd attach a small
thermocouple
to the voltage regulator and monitor it's operating temperature. Pretty cheap and easy, and shouldn't require taking anything apart to at least verify or eliminate a regulator temp issue.
