Symptoms: headlight and spotlights go off, then come back on after about 1 minute. When the headlight/spotlights are off, the voltmeter goes high, to about 14 volts.
This does not seem to happen when running only the headlight on low beam. It does happen when running the headlight on low beam and the spotlights at the same time. It also happens when running the headlight on high beam with the spotlights off.
The fact that the lights come back on suggests that this may be a circuit breaker overloading and then resetting. However, the turn signals and taillights stay on even when the headlight/spotlights are out, which suggests that it is not an issue with overloading the main circuit breaker. Also, I can't find any other circuit breaker.
Another possibility is an intermittent wire failure on the headlight circuit. I rewired the spotlights to come from the under-fairing fuse block I had previously installed, which draws power directly from the main circuit breaker. (Previously, the spotlights had been getting power from a black w/ pink wire (?)).