What fuse on a 1979 Chevy van great laker causes the headlights to turn on?

There isn't a single fuse that *causes* the headlights to turn on in a 1979 Chevy Van, or any car for that matter. The headlights are activated by the switch and the circuitry connected to it. Fuses *protect* the circuits. If a fuse blows, it's usually because there's a short circuit or an overload somewhere in the headlight circuit.

To find the relevant fuse(s), you'll need to consult your owner's manual. It will have a fuse box diagram showing which fuse(s) are responsible for the headlight circuit. There's likely to be separate fuses for the high beams and low beams, and possibly even more for related components. Also, be aware there might be a relay involved in the system.

Without the owner's manual, it's impossible to say which fuse is responsible. The fuse box might be located under the hood or inside the vehicle, usually under the dashboard.