Checking Brake Lights

For the past month I’ve been going through this brake lights saga. I had them checked, failed, had them repaired (it was with wiring), and yet the mechanic said they wern’t fixed when I took it in today for my re-inspection. How does a mechanic check brake lights, to make sure they work? How does the average “I don’t know anything about cars” car owner do so?

Not that I know anything about cars, but a couple of thoughts spring to mind:

  1. How do you check the brake lights if you know nothing about cars? Well, assuming that you don’t have someone there to look at the lights while you step on the pedal, I’ve found the easiest way to do it is at night. With another vehicle close to the back of the car, step on the pedal. You should be able to see the reflections of the working brake lights in the other vehicle.

  2. Why wouldn’t the brake lights work (according to the mechanic)? How much wiring was replaced? It is possible that in a section of the wiring that wasn’t replaced, there was a bare spot that made contact with part of the framework, and shorted out? If not, perhaps it’s a fuse, or a problem with a relay.

I check their reflection on the plate glass that fronts many businesses where I have call to park near daily.

Checking Brake Lights for Dummies

Step 1. Place key in ignition, turn to ON.

Step 2. Get brick and place on brake pedal.

Step 3. Walk to back of car and look at brake lights.
Sorry for the sarcastic reply, but it really is the easiest way. Just get something heavy to jam down the brake pedal and then take a look at the lights.

At night, back up to a light-colored wall (like a garage door or something)…with your car’s headlights off, you should easily be able to see your brake lights illuminate the wall/door with red light when you step on the pedal. The difference should even be obvious when the car’s headlights are on, really…the red light should get much brighter when you step on the pedal.

Thanks all for the suggestions. I checked them and they don’t work.

When I had them “fixed” the mechanic never told me what was wrong. I was “Sterotypical Teenage Girl Who Knows Nothing” who mechanics love to take advantage of, no doubt.

If the problem is in back of the car (light sockets, wiring), then turning on your hazards should reveal the problem. But this obviously won’t work if the problem is under the dash.

It could be a 50 cent fuse or the wire on the master cylinder might just be loose…back it up against something & look in the back. turn on any other lights too, head, turn, etc & see if they work & get back to us.

I think the best thing to do is put the car in park, press the brake, and then quickly run around to the back and try to catch 'em before they fade.

Seriously, though, have a friend press the brake while you watch. Most brake lights have more than one bulb on each side, so reflections in a window will tell you that the lights do work, but not necessarily ALL of them. If a bulb is out you can easily change them. I knew a guy who spent over $100 bucks to replace the entire light assembly when all he had was a burned out bulb. The bulbs go for less than 2 bucks. If only one light comes on, switch that bulb (which you know will work) with the others and test it again and see if it is the wiring or a dead bulb. If no brake lights come on at all, then you’ve got a wiring problem (odds are that not all bulbs would burn out together). While you’re at it, turn on your hazard lights and headlights and do a couple laps around the car.

You need to ask advice on how to check if your break lights are working? Besides what has been mentioned about looking for the reflction in nearby objects, it didn’t occur to you to have some other person tell you? Man… this reminds me of the guy who asked his buddy who was standing outside the car “does the turn signal work?” and his buddy says “now it does… now it doesn’t… now it does… now it doesn’t… now it does… …”

From my experience (at a repair shop which employed more than one person), the tech servicing the vehicle would say to another, dawdling, technician, “Hey, c’mer a minute and check the rear lights while I hit the brake pedal.” Honestly, it’s that simple. Entice a few friends over (promise 'em beer) and ask em to watch yr rear…

BTW, what kind of car do you drive? Also, were you recently in any sort of fender-bender? A crack in the brake light lens can allow moisture into the assembly and blow yr bulbs. Possibly, long-term exposure to moisture could cause damage to the wiring. Some vehicles develop problems in the thin, plastic circuit boards at the rear lights.

If it’s a recurring, serious wire problem, let it go and learn yr hand signals: A technician could spend hours of his time (and hundreds of yr hard-earned ducats) chasing after a single short along literally miles of wiring. Hope this helps.

I believe she needs to pass an inspection and I wouldn’t want to drive in city traffic very long without brake lights. I’d wager the majority of those on the road wouldn’t recognize hand signals.

Let me take my tongue out of my cheek for a second…

Don’t know where OP lives, although I would never recommend breaking (no pun intended) any local laws. In my locale, there are no inspections (not even for emissions)… Nor would I ask anyone to endanger their safety… My point being that chasing an electrical problem in a vehicle can become VERY costly: to wit, think of a mile long wire from yr electrical outlet to yr bedside lamp. Somewhere in that wire is visually undectable short that causes an intermittent flicker in the bulb. It’s up to you to find it, testing the wire inch by inch along its whole length (simplified, yes, but bear with me). By chance, you started with the end closest to the outlet. Unbeknownst to you, the short is actually all the way at the other end. Pure, dumb luck. Poor you. It takes you 15 hours to find the short. At, let’s say, $60/hour (let’s pretend that’s an average hourly rate for a mechanic) that’s $900 - before even FIXING the problem. I’ve seen customers spend more than that having a mechanic chase after electrical problems which ended up being cause by (in retrospect, at least) the simplest things.

Tell yr mechanic to cap the diagnostic time at 2 or 3 hours. If he’s still befuddled, weigh yr options and yr safety and proceed.

I’ll try to refrain from dry humor in the future…

Or just install a new wire. Not a whole new harness. Just the new wire. Maybe two. Yeah, do two, that way you’re sure. Maybe not yourself, mind you, but rather than having the shop work 2-3 hours looking for a short, they can spend one hour running the wire in an out-of-the-way location.

I just fixed mine, and it was a pushbutton switch under the brake pedal, about as long and wide as a finger. Just unscrews, and costs a couple of bucks at the dealer parts window. Worth a try.

Like I said, my example was extremely simplified…Not only is there more than just one or two wires, there are also a number of other electrical components which may fail…So you replace every single wire, sure, but then you realize that maybe it’s a shorted out relay, or the rear light circuit board (as previously mentioned)…Electrical problems in modern automobiles are definitely NOT a cut and dried issue. I’ve seen things that would make you (and your pocketbook) shudder…

To get back to the point of the OP: Get a friend over, have him watch the brake lights while you punch the pedal (or vice-versa, if he’s an inveterate liar and/or practical joker) and find out if yr lights work. Try some new bulbs (most auto parts stores can help you out). No luck? Sorry, but you gotta visit the wrench-benders.

You got me, Arturo; welcome to the board.

Brake light systems are battery to fuse box to switch under the brake pedal to wires that go to the brake lights, and that’s pretty much it (might be a relay in there to drive the current if the switch isn’t designed to handle it). If it takes your mechanic more than 2 or 3 hours to figure out where the problem is, then you need to get a new mechanic.

In my experience, a lot of mechanics are very good at mechanical things, but they don’t have more than a rudimentary understanding of electrical systems. Being an electrical engineer, I generally don’t take my vehicle to a mechanic when there is an electrical problem (the only exception was when the resistor network for the AC/heater fan burnt out and I didn’t feel like taking the dashboard off myself, and then I basically told the mechanic that part way down there that you can barely see is broke and I don’t want to fix it, so here you go) so I can’t recommend how you determine if your mechanic knows his stuff where electricity is concerned or not.

Arturo’s post shows how mechanics find electrical problems when they don’t know what they are doing, they just keep replacing parts until they get it fixed. This is very time consuming and costly. A little careful analysis with a volt meter will generally tell you exactly where the problem is within a few minutes. For brake lights that are completely out, the problem should be simple to find. For the difficult case that Arturo mentioned earlier (short circuit) all you really need is a very high quality ohm meter. If you measure the resistance between the shorted wires, you measure the resistance of the short plus the resistance of the wiring in between your meter and the short. Measure at a few key points and you should be able to determine which point is closest to the short. I’ve never been able to trace a short down to its exact location this way, but I can usually get within a few feet or so, which is close enough.

The point being you don’t replace a wire when it might be the relay. You disconnect the wire and the relay and you figure out which side has the short, then replace it.

Of course none of this helps the OP because she can’t do the electrical work herself either.

Personally, I think mechanics should get more electrical training, but that’s just my 2 cents.

I agree. The mechanics I have known have had a very good grasp of the subject (as far as I know) and had volt meters and ohm meters readily at their disposal. Even still, fiding the exact source of an electrical problem can be time consuming, although - as you correctly imply - this is typically at the front of the car, as opposed to the rear. Still, I have seen highly trained and intelligent mechanics (seriously - the kind that can debate current affairs and literaure with you right after replacing yr brake pads) spend hours chasing down an electrical problem. Sorry to divert, but felt the need to defend…

As for the OP: If you really think yr getting scrwd, ask the mechanic to explain what he’s doing and how he’s going about it all. Don’t be embarrassed – an honest mechanic will understand yr predictament and try his best to help you understand. And don’t be afraid to yank yr keys from his hand if you feel uneasy, either!