Sorry, but I am apparently not very good at google from my iPhone. Under the hood of my 1995 Monte Carlo, there are a bunch of wires behind the passenger headlight that snake past the tire well and to the back to power various things. These got ripped out a couple of years ago and home-repairs with butt connectors. Somewhere, one of them has come undone. When I opened the hood today, I found two wires that had come undone and fixed them. But my brake lights still don’t work. My tail lights do. So, instead of undoing all of them to find the faulty connection, does someone have access to a wiring diagram and can tell me what color wire to look for?
I have access to Alldata at work. Hang on while I connect remotely…
Ooof. Would it be easier to just remove the tail-light assembly and look for the color wire that leaves the brake light? Then you’ll know what wire to look for in the harness. It could also be the ground on that particular circuit is bad (rusted or broken).
Um, the other thing it could be is you might have a dual element lamp that only uses one element for the running lights and the second (brighter) element for the brakes. It’s possible you’ve burnt out the second element in both back brake lights.
Does the safety brake light still work? (the one in the back window, if your car has one)
**chaoticbear, ** I have a .jpg of the diagram. Do you want me to send it to you?
Actually, I just posted it here. It might be a little small though…
None of the brake lights come on, which leads me to think wiring problem. From the diagram, and a previous thread I posted on the topic, I see that there is a switch that controls the brake lights, and I would really hate if that had gone out. When I get back home, I’ll try poking around for a white wire under the hood in that bundle. If I had any idea how to look, I would check the wire going into the brake lights, but inal really biting more off here than I should. I an taking it to a real mechanic tomorrow if I need to so I just wanted to see if I cups find it myself and save a couple hundred bucks.
I don’t know your car, but chances are you would find this out one of two ways.
(Reminder, I don’t know your car, use common sense and if this doens’t seem to apply to your car, don’t do it).
The first thing I would do , is “pretend” like I was changing the bulb, there’s a good chance that at some point during the bulb changing procedure you’ll have access to the wire that feeds it. If that dosen’t work, you may just have to pull the trunk liner away from the trunk wall and look at the wire from behind.
Before you go tearing the car apart, go check the fuses. Looking at the diagram that Southern Yankee posted it looks like fuse 21 feeds the brake lights. (it isn’t real clear, it might be 22 or 23, but it looks like 21)
Also I highly doubt that disconnected wires behind the headlight would cause your brake lights to not work. Wrong end of the car.
If the fuses are good, the next step is to check the bulbs for the brake lights. They do burn out.
If the bulbs are good, then you have to go a bit deeper and you will need either a voltmeter or a test light.
Next is to check for voltage at the brake lights with the brake pedal depressed.
If voltage is present, then check for ground. If you have both voltage and ground at the tail light assembly either your bulbs are burned out after all or the sockets are corroded.
If no voltage is present, go to the brake pedal and check the switch for power, and see if it supplies power out when the pedal is depressed.
In other words start with the common stuff and work towards weird.
Good luck
Well, I did start with the fuse, and then I got both bulbs replaced. My suspicion for the wiring harness at the front of the car comes from the fact that when the were ripped out, I didn’t have headlights or blinkers,so that’s why I had suspected that location. I’ve never used a multimeter. Do I need to pierce the wire with a probe, or can it sense current through the insulation? (Apologies, my E&M lab was a computer program, and we never got to fool with real stuff. )
You could do that. But I think what Rick is suggesting is that you take out your bulb and test from there. Put something on the brake pedal to depress it (or turn your headlights on). Put the red lead on one of the contacts and the black on a peice of bare metal on the car somewhere.* If it lights up (or the meter moves) you’ve got power. If it dosen’t light up, try the other lead. If neither lead shows voltage, you don’t have power going to the lights. Assuming it lights up, now move the black lead from the ground to the other lead in the socket. If it lights up, you’ve got a bad bulb, if nothing happens you have a bad ground.
So in short…
If you have power and your ground is good (you get a reaction from the multimeter with both leads in the light socket) the bulb is bad.**
If that shows nothing and you have voltage from the socket to unpainted metal, you have a bad ground,
If both of those show nothing the socket isn’t getting power.
If the socket isn’t getting power or the ground is bad, you have to start tracing the circuit backwards, testing each connection until you figure out where you lose continuity.
*You can test that the ground your using to check the socket will work by trying this experiment with a known good voltage, maybe your trunk light, or any other light you can get at.
**It is also possible that the bulb isn’t bad but there is something wrong with socket itself. But since both lights are out that’s probably not the case.
PS I know this seems long an complex, but it’s a lot easier when you just go and think it through and use common sense. Think about where the power is coming from and where it should go, and find the break.
Yupp, you hit it on the head.
A couple of points however
If you don’t own a multimeter, just go to the auto parts store and buy a 12V test light. It looks kinda like a ice pick with a wire coming out the back. On the end of the wire is an alligator clip. You attach the alligator clip to a known good ground and place the tip on what ever you want to test. There is a light bulb inside the clear plastic handle, and it will light up if you have power and ground. (note: auto parts stores sometimes also sell a very similar tool for testing voltage in a house circuit, make sure you buy the 12V one. Cost should be less than $10-$15)
Don’t turn on the headlights when testing, you will only confuse yourself just wedge a stick so the brake pedal is depressed. However if your tests show no voltage at the brake light socket then go turn on the headlights and test for voltage at the socket. This will verify that you have connected your test light to a good ground, and that the test light works. Nothing worse than trying to fault trace with a dead test light.
Check the socket for corrosion. Dirty (corroded sockets can not work) Auto parts stores do sell replacement sockets. While the sockets in the trunk are prone to corrosion, the 3rd brake light socket usually does not corrode. You might also want to check for voltage there.
If you are unsure about the checking at the socket, look at the back of the light assembly, according to the wiring diagram the left brake light has a yellow wire, and the right has a green wire. You can either pierce the wire or follow it to a connector and slip your probe into the back of the connector to touch the bare metal inside.
If your tests show no voltage at the sockets, the next most likely source of failure is the brake pedal switch. It should be on the arm for the brake pedal. Power comes in on the orange wire (should be hot all the time even with the key off) and when the pedal is depressed power should also be at the white wire.
I am assuming that your car has a dual filament tail brake light bulb. if you look closely at the light bulb there will be two connectors on the bottom (usually lead) and the base is brass. One of those connectors is for the brake and one for the tail lights. on the side of the bulb are two pins that are offset in height from the base of the bulb. Look at the socket there are two slots that are also offset in height. The shorter of the vertical slots is supposed to have the pin on the bulb that is closest to the glass of the bulb. It is supposed to be fool proof, but I have seen people install them incorrectly.
In order of probability your fault sources are:
Bad bulbs
Bad fuse (check it with the test light just to be sure, also make sure there is voltage at the fuse)
Bad switch
Corrosion / bad sockets / bulbs installed backwards
Bad harness connector
wiring fault
I hope this is clear, I just woke up and haven’t had much coffee yet. If you have questions feel free to get back to me.
Damn missed the edit window. On testing fuses I wanted to add this:
If the fuse is good the test light will light on either side of the fuse. If the fuse is bad only the incoming side of the fuse will light. If neither side lights up either your test light isn’t grounded, or you have no voltage to the fuse. Test around the fuse box. If the light doesn’t light up somewhere, you don’t have the test light grounded. If it does light up sometimes, but not at fuse for the brake lights, you have a voltage supply problem.
Testing the voltage light to make sure it works can be done right on the battery terminals. Clip the alligator on the negative terminal and touch the volt sensor to the red post and you should have the light come on.
Then continue on your merry way.
If you want to make sure you have a good ground during all your testing you can clamp a wire extension (10 feet of wire or so) to the negative battery terminal and then attach the alligator clip to the end of that wire. Then you’re certain of getting a good ground.
The bulbs and fuse have both been replaced, so next is the switch, I guess. I haven’t tested it recently, but the cruise control has always been iffy, and I don’t think it works any more, and some one-off answer on something I googled mentioned there might be a connection.
I took it to my mechanic this morning armed with all of this knowledge, and he said he couldn’t find anything wrong with the front wiring harness, and said that I should take it to the dealer if it’s a more complicated electrical problem. No way am I going to do that unless I have to, because I don’t have $infinity to spend on the problem. Next Wednesday is the next time I’ll have any time to look at the thing during daylight hours; I work and go to school during every other daytime hour. Except maybe Sunday morning. If I get out there and mess with the brake switch, I can’t possibly cause any more damage, right?
Thanks, btw everyone.
If the rear turn signals work, it’s not the bulbs, the sockets, or the wiring to them. It could only be the fuse (#23), the brake light switch, or the wiring to those items*. If the fuse is good, it’s almost certainly the brake light switch.
The switch is on the brake pedal support by the top of the brake pedal lever, kind of a pain to get to. It has an orange power-in wire which should be hot at all times. The output wire is white, which should become hot when the brake pedal is depressed slightly.
*This is assuming the high center brake lamp is not getting power. If it is getting power and its socket or bulb is faulty, then the brake light switch is okay, and the problem is in the turn signal switch.
Update! (sorry, internet access has been spotty while I’m waiting to fix my main computer)
After I went and picked up my car from the shop guy on Friday, he mentioned that it wasn’t the brake switch, because then they would be stuck on. Any truth to this?
Also, from the combination of me playing with those wires and him playing with them, my front right blinker doesn’t work very well (is dim), and my car recognizes it because my blinker blinks fast. Also, when I have my right blinker on and hit the brakes, the left brake (or tail, I can’t tell) also comes on, giving the illusion that I have brake lights, but only when I have the right blinker on. Also (lol), when I pull the high-beam/blinker stem toward me about half-way, with the headlights on, the back lights brighten liek brake lights.
At some point, if I get some spare time this week, I’ll post a picture of how terrible that group of wires looks, and you’ll all laugh.
You have a bad ground in the system. I would have to study the turn signal and brake light circuits to find out where, but the right front would be the place to look. Also it would appear that the high beams are also feeding back somehow to the brake circuit.
Off the top of my head, I would guess that the highbeam on the right side, and the RF turn signal share a ground and that ground is bad.
Fix it, and part of your problems will go away.
Sigh. How can people be so f*cking stupid?
ONE way the brake light switch can fail is to be stuck on, but it’s certainly not the ONLY way it can fail. I’ve seen plenty of those switches that failed so that the brake lights didn’t come on. That this guy earns his living fixing cars is a sad commentary on the state of the auto repair field, and unfortunately it’s not that uncommon. Take it to someone who’s actually competent for any further work, and I bet your problem will be resolved in short order.
Anyway, short answer to your question, no, there’s no truth to that claim.
These types of situations can always be understood in terms of the wiring diagram once the fault is found, but it’s usually quite difficult to solve them “on paper” without first physically testing various components.
Rick’s conjecture may well be correct. My first thought on reading the symptoms described above was a faulty turn signal switch. It’s a pretty good bet the problem lies in one of those areas.