Common automobile fuses are rates 32v, so they work in cars and trucks. A 12v nominal car voltage may be 14.5v plus depending on the alternator, so a truck alternator would be almost 30v under some circumstances, hence the 32v rating.
How many lights you can string depends on the power factor of the complete fixture.
Also, car fuses are fast blow. If you switch all the lights on at once the surge will be much higher than the operating current.
A Turnigy power meter measures peaks, so it would tell you the peak current required to start.
