For the 1999 Ford Explorer, the low-beam and high-beam headlights both use 9007 bulbs. This means one 9007 bulb type covers the main headlight functions listed for this model year. The fog lights use H1 bulbs.
Other useful exterior fitments include 3157A bulbs for the front turn signals and parking lights, 916NA bulbs for the front side markers, and 3156 bulbs for the rear turn signals and reverse lights. The brake and tail lights use 3157R bulbs, while the center stop light uses a 912 bulb.
For lighting inside the Explorer, the dome and engine-area lights use 906 bulbs. Map, interior, and license-plate applications are listed with 168 or 917 bulbs, while the glove box, instrument, high-indicator, and turn-indicator applications may use 194 or 7441 bulbs. Check the original bulb and socket before ordering where multiple fitments are listed.