Q: Headlight flickers, then goes completely out

If the vehicle has conventional halogen headlamps, then I’d look for a loose or broken ground to the headlights, either at each individual headlamp, or the headlamp circuit. If the vehicle is equipped with HID (high intensity discharge) headlights, then there may be two possibilities. The HID bulbs themselves may be bad, but the second part - the ballasts, or ignitiors, for the bulbs may be bad. HID bulbs do not have a metal filament like halogen bulbs. They are filled with xenon gas. This gas requires a lot of voltage to light off. The ballasts, take the 12 volts from the vehicle and amplify it to 35,000 volts or more. That’s why HID bulbs kind of look like a flash bulb when they first light, then take a moment or so to achieve full brightness. Once lit, they only require about 35 watts to maintain their brightness where halogens require 55+. You can try replacing the headlight bulbs first. HID bulbs are not cheap but they’re less expensive than the alternative. If the ballasts are bad, they are part of the headlight assembly. Very few - if any - manufacturers offer the ballast as a separate replacement part. You’d most likely have to replace the headlight assemblies.