It may be really obvious, but l have not been able to figure it out yet. Any ideas?

simple...get a bat and smash the headlights..

Hmm - l have an '02 XL-7 (nearly the same vehicle) and the only time my headlights turn off is when I've started the vehicle with the emergency brake pulled up in the locked position. The moment you unlock it, the lights come on - l believe it is an industry standard, so there may not be a way if you've already looked it up or reviewed the CD disk manual. sorry l could not help more with this one - but it may be standard now - as most are.

Suzuki Vitara
1. Unplug the DRL module located under the dash to the right of the steeering column. It is a small silver box with a multi pin plug in its side, pretty obvious.
2. Lift the circular light sensor on the right side of the dash. Unplug it. Do not drop the plug into the dash. Retain it and be sure to secure it with a string attached to the sensor housing so it can be recovered if need be, and does not rattle
Easy as that!