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About a month ago my brake lights quit working. I've replaced the bulbs, but that didn't fix it. I've checked the inside fuses, and they are fine. The fuses under the hood look fine, but when I test them with an ohm meter, there is no power.
I've been having alternator/battery issues so I thought that maybe there was a short somewhere along the wiring for the brake lights, but I did not find one. I'm going to go ahead and replace the alternator this weekend (hoping I can do it myself!). Could the alternator be causing the brake light issues?
 

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Wait!
It is doubtful the alternator is causing the brake light issue.
Didn't say can't ... but highly doubtful.

Next, Ohm meter is not used to check for power, usually.
The voltage part of the meter is used.
Working with cars usually mean 12 volts so the scale is set to 20 volts
It should be able to measure anything less than 20 volts.

Fuses can be check with the ignition key on and engine off
Also need someone to step on brake
Volt meter has one end connected to ground
The other side is used to probe the little tabs on the fuses.
Each fuse should have two tabs. Touching one side at a time should show both sides have voltage (12 volts).
If not then take out fuse and check.

Hopefully it is just the fuse.
If not then come back and update us.
We will try to help further.
 

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I assume that you really meant a multi-meter, and not just an ohm meter. I hope that you had it set to DC volts when checking fuses still installed in the car. You want zero volts between the two test points on the top of each fuse, otherwise the fuse is blown. You can check between ground (metal part of car) and the fuse test points to see if power is getting to that fuse. If you remove the fuse from the car, then you can use the ohm setting to test the fuse. A good fuse will read really close to zero.


Did you test for power at the brake light switch?



It's very unlikely that the alternator is related to the failure of the brake lights. (We are talking about the brake lights at the back of the car, and not the brake warning indicator on the instrument cluster, correct?)
 

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If there is no power to the fuse
then checking the potential between the tabs at the fuse would show zero volts
Would it mean the fuse is good?

I believe it is better to check against ground
This way the meter shows whether there is voltage at the fuse

Of course, each has their own way of doing things
One isn't better than another ... just different
 

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Dvom
 
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If there is no power to the fuse
then checking the potential between the tabs at the fuse would show zero volts
Would it mean the fuse is good?

I believe it is better to check against ground
This way the meter shows whether there is voltage at the fuse

Of course, each has their own way of doing things
One isn't better than another ... just different

I do not disagree, and I did point out how to check for power at the fuse. If you have no power at the fuse, testing both sides for voltage to ground also would not tell you if the fuse is good or bad. In either case, you would have to have both power and a load to know for certain that the fuse was bad. You would know if you had power, but you wouldn't know if you really had a load or not.

If you have power at the fuse, but no load both tests still wouldn't always show a bad fuse. If you want to be 100% sure, you have to take it out of circuit and do a continuity test on it. (Of course, if you have a fairly bad meter, it would supply enough load of its own. I am assuming the use of good test equipment, which is likely a bad assumption.)



I'm betting on the switch or bad bulb sockets anyway.
 

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... you would have to have both power and a load to know for certain that the fuse was bad. You would know if you had power, but you wouldn't know if you really had a load or not.
Agreed

If you have power at the fuse, but no load both tests still wouldn't always show a bad fuse. If you want to be 100% sure, you have to take it out of circuit and do a continuity test on it. (Of course, if you have a fairly bad meter, it would supply enough load of its own. I am assuming the use of good test equipment, which is likely a bad assumption.)
I hate continuity tests.
You're right about needing a load.

Never know about good or bad test equipment.
Sometimes a a test light is all you need??



I'm betting on the switch or bad bulb sockets anyway.
I quit betting a long time ago.
Use to watch the three card monty.
Gambling is not for me. But I don't know why I keep buying Lottery tickets????
But, you are probably right about the switch.

Comment: The ignore function on this forum is a blessing.
 

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About a month ago my brake lights quit working. I've replaced the bulbs, but that didn't fix it. I've checked the inside fuses, and they are fine. The fuses under the hood look fine, but when I test them with an ohm meter, there is no power.


I assume you mean a dvom...digital volt ohm meter. How did you test them?


I've been having alternator/battery issues so I thought that maybe there was a short somewhere along the wiring for the brake lights, but I did not find one.



How did you test for that?


I'm going to go ahead and replace the alternator this weekend (hoping I can do it myself!). Could the alternator be causing the brake light issues?
Alternator is not causing your brake light issue. How old is the battery? Why are you replacing the alternator? Did you check the brake light switch? If so, how?
 

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About a month ago my brake lights quit working. I've replaced the bulbs, but that didn't fix it. I've checked the inside fuses, and they are fine. The fuses under the hood look fine, but when I test them with an ohm meter, there is no power.
I've been having alternator/battery issues so I thought that maybe there was a short somewhere along the wiring for the brake lights, but I did not find one. I'm going to go ahead and replace the alternator this weekend (hoping I can do it myself!). Could the alternator be causing the brake light issues?


Before doing anything we need to find out what type of test equipment is being used.
If it is an arranging digital meter and the ohm range is selected, then ok. If it is not auto ranging ensure the 0 to 200 ohm range is selected.
Remove wire terminals from brake light switch and place both multimeter probes on the switch terminals.
The switch will not provide any reading on the meter but when the brake pedal is pressed firmly the meter will show a low ohm reading.
If no reading is obtained the switch is defective and requires replacement. This assumes that you have checked for 12v supply at the fuse ensuring that you have a verified good ground/ earth and the same test had been carried out at the brake light switch.
For non electronic and airbag circuits I prefer to use a quality analog multimeter for ease of instant viewing.
Please keep us informed of your progress
 

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Hi

Hyundai Australia had a recall because of faulty brake peddle switches a few years ago.
I'd suggest checking the switch on the brake peddle based on that.
They don't fit different switches just for us down under.
 

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The brake light switch is the problem. It is not the alternator. If the directional signals are working then you have power, even more so if your brake and signal lights use the same bulb but different filaments. On modern cars, the brake light switch is usually on the brake pedal arm under the dash. The switch is no good or one of the wires to the switch has been damaged.
 

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It’s the brake light switch. There is a recall. The new switch is a little smaller. If you have adjustable pedals, it’s a pain to do but can be done without disassembly.

I had to crunch the old switch up with some pliers to get it out. The new one can be squeezed in with a little scratching of the case.
 
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