What headlight bulbs do i buy

Buy a two pack of the low beam bulbs and change both had lights. the voltage drop will burn one out since they have different resistance.

in low beams or high or both?
that is caused by:
1: bad held lamp. old lamps can go dim.
swap left and right, if dim follows bulb, bingo weak bulb or wrong type bulb. buy matching blubs (same brand and P/n)
2: bad wiring to lamp. damaged wires, or connectors to same.
4: bad combo switch. (if low beams)
5: bad fuse or holder, corrosion , to either.
head lamp fuses. there are 2. left and right.
6: hackers, many hackers put in wrong lights. inspect it.

there is a grove so the bulb only goes in one way look for the different spot on the side of the bulb

look inside owners manual in glove compartment look up bulb replacement in the back index it will show and tell you how to replace headlight bulbs. be sure to wear clean gloves, because headlight bulbs or halogen type bulbs, if oil from hands or skin touch the halogen bulb it will cause halogen light bulb overheat and blow out.you can go by auto parts store when you buy new headlight bulb the salesperson will go out to vechicle and replace headlight bulb for you wont charge you any thing.just charge you for the headlight bulb.

9006.

It is fairly simple to change your headlight bulb. First you need to buy a replacement bulb - typically the auto store will have a catalog with different models for your bulb. (Different brightness usually) My replacement bulb had the model 9004.
DO NOT TOUCH THE GLASS OF THE BULB WITH YOUR HANDS - the oil on your hands will cause the halogen bulb to burn out faster. You should be able to handle just the plastic part in the rear of the bulb.
Remove the old bulb (at the back of the headlight assembly) by twisting off the circular "cap" that keeps the bulb in. You can then detach the bulb socket and remove the old bulb. Insert the new bulb carefully and attach the bulb socket. Then twist the cap back on.
Good luck!

Raise the hood and lean forward, look at the back of the headlight assembly. To remove bulbs from the assembly they are turned 30 degrees and pulled straight back, unplug the wires. Do not touch the new bulb glass, hold them by the base. If you are using a lot of force you are turning them the wrong way. Buy correct new bulbs and bear in mind they look the same and fit in the same hole but the bulbs fitting the left and right side of the assembly are different.

Is the focus of the headlight incorrect and should be adjusted?
Have you checked the reflective surfaces to ensure they are clean and the headlight glass is clean?
And finally - maybe the other bulb is of higher quality/light output. I notice a significant difference between different brands of bulbs sometimes.

Try swapping the headlight bulbs or buying a known good bulb and testing that way. Sounds like a shorted bulb filament issue.

Unless the engine compartment in your '99 is drastically different from my '96, I disagree. I've changed both of my lamps and the battery didn't have to come out. You just have to take the headlights loose to gain access to the rear of them. The lamp holder just unscrews and pops right out. If nothing else, pick up a Haynes or Chilton manual for your car. It has exacting instructions on how to change the lamp.
For what it's worth, If your headlights are hazed over like many older cars, don't buy the exact factory replacement lamp. It' won't be bright enough. Buy a higher lumen bulb.