Worry about my car tail lights or not?
September 13, 2007 10:23 AM   Subscribe

Should I worry about my car tail lights or not? I have a 98 Saturn station wagon (150K+ miles, I've owned it all this time) and today when I took it in for inspection, they told me the brake lights - in fact, all the tail lights - weren't working. Then, 30 seconds later, they worked fine.

A couple people have told me, over the past year or so, that I had a tail light out. When I went in today, I told the guys to go ahead and replace the tail light. Well, they brought the car into the shop and then came out and told me, "Hey, you have no brake lights! No lights at all back here!" This, obviously, scared me and then, 30 seconds later, they tried again and the brake lights - and all the tail lights - worked fine. So they passed it but now I'm worried.

The car has pretty much always had some weird fuse/electrical issues: the brights light on the dashboard flashes on and off randomly, as does the alternator light and the dome light hardly ever works then suddenly, it will work for a day or two before going away again. This is the first time that these issues have migrated to the outside of the car, though.

Is it possible that I have some kind of weird electrical thing going on whereby my tail lights work sometimes and sometimes don't? Should I be worried about this possibility? Should I take the car somewhere (where?) to check this out? Should I check it out at home with a friend? How? I really, really don't have any extra money right now so I'd very much prefer to avoid spending any but, OTOH, no brake lights is pretty serious - IF it's happening.
posted by mygothlaundry to Travel & Transportation (12 answers total)
Yes, it's possible that they sometimes work and sometimes don't. A frayed set of wires or a bad connection, for example, might produce that result. If you've got a place in town that specializes in automobile electrical systems, take it there. If not, either a car-audio place (they do a lot of electrical work) or a trusted mechanic. If you've got a friend with a multitester, or one who messes around with cars, it wouldn't hurt to ask them to take a look at it.

And yeah, I'd say it's at least a little bit serious, and I'd worry about it if I were you. Brake lights are pretty important for signaling other drivers and avoiding accidents and whatnot, and, just as importantly in my mind, not having brake lights will vastly increase your chances of being pulled over.
posted by box at 10:29 AM on September 13, 2007

You have either a bad ground for the lighting system(s), or something wrong with the battery/body ground. I would suggest:
1) removing the cables from the battery, then running a battery brush on both the cable ends and the battery terminals.
2) Take off, clean/brush, and re-mount both ends of the + cable, the - cable to the engine, the + cable (smaller) to the fuse block/relay, and the - cable to the body (usually with a star washer.

You can buy a small "batterybrush" from any auto parts store.

Also, make sure the cable ends are ALL THE WAY on the battery terminals. Loosen the bolts more than you think you have to, and if necessary, use a hammer to get them to completely seat on the battery posts.

Also, if the fuse block has a separate wire to body/frame ground, make sure it's tight and has good connectivity.
posted by notsnot at 10:31 AM on September 13, 2007

When nebulous electrical problems occur, it is common sense to check the condition of the battery and alternator connections, including taking them apart, cleaning them with wire brushes, reassembling them tightly, and coating the cleaned connections with dielectric grease, particularly the battery terminals. If you find any substantial corrosion at the battery terminals, you should also carefully clean the battery case, and inspect very careful for cracks, especially around the terminals. For a car battery more than 2 years old, there is a high probability that minor cases cracks, particularly in the areas where the connection posts penetrate the case, allow sulphurous corrosion of the battery connections. Also, batteries can fail internally, by mechanical action, when their internal plates and plate seperators breakdown. You should have your battery and charging system tested, (usually for free at any Autozone or other chain auto parts store). Replace the battery if indicated.

If you're absolutely sure your battery and charging system are up to snuff, then look for corrosion in the sockets of your tail lamp bulbs, particularly if you see any evidence of water vapor in your tail light lenses. Many cars have poor weather seals or cracked tail light lenses, which allow water vapor to collect inside the lights, contributing to corrosion in the metal bulb sockets.
posted by paulsc at 10:42 AM on September 13, 2007

I lost my brake lights a couple months ago and didn't know it until a truck nearly rear-ended me in traffic...so just on that alone, I fixed them. Turned out that the relay switch on the brake pedal itself went bad. Cost me $25 and 15 mins to fix. Plus, it's a big red flag for the Police to stop you....
posted by keep it tight at 11:04 AM on September 13, 2007

there are many possibilities here. It could possibly the relay that turns the lights on. Maybe the realy and/or fuse needs to be removed and then re-inserted (to sort of clean off corrosion). It could be frayed wire or bad grounding. The issue being intermittent points most toward the last two. also, one of my taillights (on a 99 Grand Am) went out once because the connector at the bulb had vibrated off of its connection, even though they aren't supposed to do that.

if you need to drive this car with the taillights out, I think most states allow you to use the standard hand signals (probably daytime only though), so that you don't get it trouble. check out your state's Driver's Handbook/DMV website.
posted by ArgentCorvid at 11:05 AM on September 13, 2007

Check for water in the trunk, e.g., in the spare tire well if there is one.
posted by SNACKeR at 11:06 AM on September 13, 2007

I don't think it's a ground, as that would usually only affect the lights on one side or the other. And I don't think it's a battery or alternator issue, as that would interrupt power to the computer and stall the engine. Individual socket problems would also only manifest themselves on one side at a time.

It sounds like one of the main wiring harness connectors is loose. Essentially, each part of the car has its own wiring, and when the parts are joined, the wiring harnesses meet up at big junction connectors. If you remove the engine, then, you just disconnect a few things and it comes right out, with all the sensors and stuff still in place, for example.

The Haynes (Chilton's) manual for your car will have wiring diagrams in the back, and the tech staff at the auto parts store can give you a 5-minute rundown of how to read them and what you're looking for. Junction connectors will look like a bunch of wires indicated like so:

red/yel           blu

grn/wht           grn/wht

The arrows indicate the connector, and in this example, one wire changes colors at the connector, the other remains the same colors when it picks up on the other side.

Physically, these connectors look like plastic blocks and they usually meet at a bulkhead somewhere. A screw pulls the two sides of the mess (say, the engine side and the interior side) together. If that's loose, it would cause the problems you describe.

Also, it could be something in the fuse box. Lay a brick on the brake while you wiggle all the fuses and relays in front, and wires in back, of the engine-bay fuse box and the interior fuse box. (Most cars have at least two fuse centers now.)
posted by Myself at 11:14 AM on September 13, 2007

they told me the brake lights - in fact, all the tail lights

This suggests that either the power feed to the rear lights or the earth is loose. Assuming the power is switched at the pedal end of the car (as is usual - brake switches et al 'make connection' and allow power to go to the light), then the only thing common is the earth.

As pointed out, checking/cleaning the earth terminals is a good thing to do. Being as it only affects the lights, checking the little earth straps inside the boot area for corrosion is worth doing (they'll be between the light unit loom and somewhere in the body). Again, cleaning and checking should work. There may be some other sort of earth straps near the relevant fuses, too. Check that.

It doesn't sound like anything serious, to me, just something that might be a little bit annoying and time consuming to fix.
posted by Brockles at 11:21 AM on September 13, 2007

NB after posting:

US cars may be wired differently, but a common earth connection for all rear lights is not unheard of in my experience - 1980's Fords were notorious for flashing all the lights and randomness when the cars started to corrode and earths went south...
posted by Brockles at 11:23 AM on September 13, 2007

I can't offer any advice on what might be causing the problem, but it looks like the guys have covered that pretty well above. I'm chiming in to say that it's definitely worth it to get it fixed. I've been in traffic behind cars without working brake lights several times, and was amazed and horrified to find how much my brain relies on them to decide when I need to brake. The car in front of me would slow down, and even when I was aware of the situation it would take an extra second or two for me to hit my own brakes. My brain just didn't register "getting too close" because there were no lights to tip it off. A rear-end collision seems practically inevitable.
posted by vytae at 12:00 PM on September 13, 2007

It's almost easier to fix them than to worry about it:
Replacing brake lights in a Saturn
posted by misha at 5:24 PM on September 13, 2007

Is it possible that I have some kind of weird electrical thing going on whereby my tail lights work sometimes and sometimes don't?

Oh yes. Have you ever towed anything? If you rewire so you have a standard tow package pigtail thingy for the trailer lights, and don't do it right, you can end up with all sorts of counterintuitive behavior, from partial left blinkers and partial right blinkers to "on" meaning "off". (Been there, done that.) The modern automobile is a wondrous thing, but to minimize wiring labor and materials, they design all the lighting in a very certain arrangement, whereas electricity is very amenable to shortcuts and interruptions. That can happen intentionally (trailer lights) or unintentionally (friction short). It can also happen when somebody does something you don't think should have affected things this way, like replacing the automatic window motor (for example, though usually that's something that would be on a separate circuit).
posted by dhartung at 8:21 PM on September 13, 2007

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