This page last modified:
April, 2005


Lights out!

How many engineers does it take to change a light bulb? I don't know, but if you can think up a good answer to that question I'll be happy to give you credit on this page. Guess what, someone did it! csrobin4 (whoever that is) said this: "If the bulb had been engineered properly in the first place it wouldn't have burned out!"

One of the easiest repairs you can make on your car is to change a light bulb. In most cases all you need is a screwdriver or two. If you're just starting to repair your car, a burnt out bulb is a good first project.

Where I live (and probably where YOU live as well) a police officer can stop your car and write you a ticket if one of the lights doesn't work. A ticket that is worth $75.00. Then, after you have fixed the light, you have to get a complete vehicle inspection to make sure that the rest of your car is safe. That costs at least $50.00 Guess what? The inspection almost always finds some other thing that isn't quite good enough, which you then have to get fixed, which costs still more money, then you get to get inspected again... Can you see how a burnt out light bulb can cost hundreds of dollars?

Professional drivers, before every trip, perform something called a pre-trip inspection. This involves walking around the vehicle, checking all of the lights, the wipers, the tires, the brakes, checking for oil leaks, etc. It only takes a minute or so, and saves them a lot of money in the long run. You think your repair bills are high? These guys' bills are into 4 digits on a regular basis.

If you find a single tail light or turn signal that doesn't light when you check, it is probably due to a burned out bulb, a relatively simple fix. Usually.

The problem resolves itself to three, no, four, smaller problems;

Expose the bulb

This part of the job can vary from simply reaching up behind the light fixture itself and twisting the socket out of the fixture, to removing forty pounds of plastic trim panels, the bumper, the grille, etc. It's not always obvious how to get to the bulb.

Remove and identify the bulb.

Usually just a 1/8 turn twist to the left, and the bulb pops out into your hand. Sometimes, on newer cars, they just pull straight out.

Procure and install new bulb.

Most of the time the part number is written or stamped right on the base of the bulb. Just go to your friendly neighborhood auto parts store, lay it down on the counter, and say "Got one of these?" They will.

Put it all back together.

You were paying attention when you took it apart, weren't you?



The vast majority of the time, a light that doesn't light up is due to a burnt out light bulb. All you need to do is put in a new one. If you are working on a tail light, look at the lens. Can you see the screws that hold the lens to the back of the car? They are usually recessed into the corners of the lens. Remove them and one of two things will happen; either the lens will come off, or the whole light assembly will come out. If the lens comes off and you can see the bulb, push gently on the bulb and give it a gentle twist to the left (CCW). If it rotates about 1/8th of a turn, it should pop right out into your hand. Be very careful, the glass is very fragile, (duh) and if it breaks when you are pushing on it you can get a nasty cut. I know this from experience. (Wanna see my scars?) If it doesn't twist, pull gently on it and it should slide straight out. If neither of these techniques work then you have a problem, the bulb is seized or rusted into the socket and will take a little more effort to replace. Skip ahead to problems.

The suits have only come up with two ways to keep the bulb in the socket so far, but you have to figure out which one you are dealing with before you start. The oldest one is the "bayonet mount" in which there are two small pins on the circumference of the brass base of the bulb, and two grooves in the socket that the pins fit into. There are two types of bayonet mount, uneven, where the pins are at different distances from the end of the bulb, and even, where the two pins are opposite each other, the same distance from the end. The uneven type is only found on bulbs with two filaments. A bulb with uneven pins will slip into the socket in two ways, only one of which will allow it to twist that 1/8th of a turn clockwise that locks it in. Don't force it, if it doesn't want to twist, pull it straight out, rotate it 180 degrees, and try again, it should go in and twist easily that important 1/8th of a turn.

I'm not sure what they call the new way of combining bulb and socket, but it is perfect. The bulbs have plastic bases, and so do not corrode into the socket. It is impossible to insert one incorrectly. The new system solves virtually all of the problems that occured with the old system due to people putting the wrong bulb in the socket and with people putting the bulb in incorrectly. It also solves the problem of the bulb base corroding itself into the socket. Finally, the suits got something right.

Common Lighting Problems


What If?Ken Says:
No tail lights or
front park lights

You've probably blown a fuse, find it, replace it, and if it doesn't blow instantly, you're on the road again. If it does blow instantly, you have a dead short. That's a short circuit to ground of one of the hot wires that go to one of the sockets.

Turn signals don't blink, or blink slowly or quickly.

Probably need a new flasher, find it, replace it and go. (Be aware, there are TWO flashers in most cars, one for the turn signals, and one for the hazard warning lights.

BOTH Front turn signals come on when you brake.

Seen this one a few times, it has always been the hazard warning flasher is broken or missing and the hazard warning flashers have been left turned on.

One tail light is brighter than the other.

This one has a couple of possibilities, the usual one is a broken ground wire or a bad socket ground at the affected light. I have also seen this when someone jammed a bulb in backwards and somehow managed to get it to light the wrong filament.

Tail lights work, brake lights work, but when I brake with the lights on, one or more go out.

Another easy one, bad ground at the rear sockets. Replacement socket assemblies are available for most cars, and that is often the easiest fix. Maybe I shouldn't say this one is easy, my next door neighbor has this problem with his VW and even though he's not a total idiot, he can't seem to fix it even though I've told him several time exactly what is wrong.

No headlights on high (or low) beam, or no headlights at all.

Probably the dimmer switch. They come in a few varieties, the floor-mounted one, for older cars, costs about 10 bucks, lasts almost forever, and is a snap to check or change. The second kind, costs 20-40 bucks, mounts on the steering column below the dash, lasts for a while, and is a bit more trouble to check or change. The third kind, the newest, costs a few hundred dollars, mounts under the steering wheel, is a pain to test, and can be a nightmare to change. The suits strike again.

The glass part of the bulb came loose from the base.

Go ahead and twist off the filaments and discard the glass portion. I've heard that a potato works for removing what's left, but due to a shortage of potatoes around the shop most days, I use a big screwdriver or a special pair of snap-ring pliers that open when you squeeze the handles. A good shot of penetrating oil can sometimes help to loosen a corroded-in base. The key here is patience. Look closely at what you have, give it a good shot of penetrating oil, and carefully work it back and forth until it moves freely. Once you have it moving, give it that 1/8th turn to the left and gently pull the remains out of the socket.

One headlight out, on high or low beam.

Usually just a bulb, not too tough, but there is one thing that you must be aware of... the aiming screws are usually very close to the screws that hold the bulb into the headlamp assembly. If you screw up the aiming screws it is almost impossible to get them back in the right position without a proper headlight aiming device. If you are dealing with a rectangular headlight, the screws you want are the two at the top and the two at the bottom of the chrome ring that goes around the edge of the lamp. Just remove these, (careful, it is easy to strip the slots that the screwdriver goes into) then take off the chrome ring, pull the bulb out just far enough so you can unplug it, and put the new bulb back in. Note: there is a right side up, and it is possible to put a headlamp in upside down. If you are dealing with a fairly new car, the bulb is accessed from the BACK of the light, which can be a hoor to change in a small car because you may have to remove the battery, windshield washer bottle, etc. to gain access to the bulb.

I changed the bulb but it still won't light.

OK, the first thing you need to do is determine whether there is power to the socket. To do this you will need a "test light" which is a tool that has a light bulb with a ground wire attached to one end and a test probe attached to the other. Looks sort of like an ice-pick with a wire coming out of the handle. You can make one, but they only cost a few dollars and every parts store should carry them. Attach the clip on the end of the wire to a good ground, and touch the pointy end to one of the little contacts at the bottom of the socket. It should light up. If it doesn't, you've got a wiring problem. Someday there will be a page here to help with those...


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