Don't know about that specific camera, but what you want is to get it into a full manual mode, so that you can try different combinations of exposures and apertures. Keep the flash off.

If the camera doesn't have a full manual mode, you basically have to fool it by locking the automatic exposure using another target, then move the camera to aim at the headlights.

The tripod is a good idea.

Sample below was shot with a digital camera, in fully manual mode; I just worked at it until I got it right.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue