How to use a multimeter
08-07-2012, 10:30 AM
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How to use a multimeter One thing that always gets me when working on a vehicle is when something goes wrong somewhere with a wire. I swear I'd rather have the engine blow up because at least I know where the damn problem is and how to fix it. I've never used a multimeter and want to learn how. Anybody know any really good informative links on this?
08-07-2012, 11:34 AM
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Just type "multimeter tutorial" into google and there are plenty of good links, documents, and videos.
The main functions you will use are voltage, resistance, and continuity. Measuring DC current is trickier and requires putting the meter in line with the wire. Clamp meters only measure AC current.
Fluke is probably still one of the best brands out there but any basic digital unit will serve most automotive troubleshooting needs. Get a digital unit, though, well worth the expense over an analog one.
The main functions you will use are voltage, resistance, and continuity. Measuring DC current is trickier and requires putting the meter in line with the wire. Clamp meters only measure AC current.
Fluke is probably still one of the best brands out there but any basic digital unit will serve most automotive troubleshooting needs. Get a digital unit, though, well worth the expense over an analog one.
08-07-2012, 02:55 PM
#5
(This will probably get a bunch of "experts" yelling at me)
You should probably start with a simple test light. There are a limited number of circuits that you wouldn't want to use a test light but they are mostly computer (PCM) and gauge related (oh, and one big one - the airbag - never use a test light on the airbag circuit). Other than that, a test light can be an extremely useful and easy-to-use diagnostic tool.
Most of the time you will be trying to determine whether power is available where it should be or whether a circuit has a good ground. Those are the two most basic issues you will experience with electrical problems. It's very simple to use a test light to determine those things.
For example, suppose you have a problem with your front turn signal. Turn your ignition and turn signal on. Use your test light at the front lamp to see if you get flashing power on the blue wire. If so, the problem is the socket or bulb. If not, move up the circuit to the DRL module behind the radio. Use your test light to test for flashing power on the blue wire there. If so, then you know you've got a break in the blue wire somewhere between there and the front lamp. If not, use your test light to check for flashing power at the blue with white stripe wire going into the DRL module. If so, you know the DRL module is the problem (power is going in but not coming out). If not, move up the circuit to the turn signal switch wires at the base of the steering column... you get the idea.
I always start with a test light before getting out my multimeter. In fact, I use one so often that it was worth it for me to buy the advanced Power Probe III test light that sells for about $100. But you can get a basic test light for under $10.
There's good information about test lights here: http://www.bcae1.com/testlite.htm
The same site also has good information on multimeters: http://www.bcae1.com/vomillia.htm
You should probably start with a simple test light. There are a limited number of circuits that you wouldn't want to use a test light but they are mostly computer (PCM) and gauge related (oh, and one big one - the airbag - never use a test light on the airbag circuit). Other than that, a test light can be an extremely useful and easy-to-use diagnostic tool.
Most of the time you will be trying to determine whether power is available where it should be or whether a circuit has a good ground. Those are the two most basic issues you will experience with electrical problems. It's very simple to use a test light to determine those things.
For example, suppose you have a problem with your front turn signal. Turn your ignition and turn signal on. Use your test light at the front lamp to see if you get flashing power on the blue wire. If so, the problem is the socket or bulb. If not, move up the circuit to the DRL module behind the radio. Use your test light to test for flashing power on the blue wire there. If so, then you know you've got a break in the blue wire somewhere between there and the front lamp. If not, use your test light to check for flashing power at the blue with white stripe wire going into the DRL module. If so, you know the DRL module is the problem (power is going in but not coming out). If not, move up the circuit to the turn signal switch wires at the base of the steering column... you get the idea.
I always start with a test light before getting out my multimeter. In fact, I use one so often that it was worth it for me to buy the advanced Power Probe III test light that sells for about $100. But you can get a basic test light for under $10.
There's good information about test lights here: http://www.bcae1.com/testlite.htm
The same site also has good information on multimeters: http://www.bcae1.com/vomillia.htm
08-07-2012, 07:43 PM
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(This will probably get a bunch of "experts" yelling at me)
You should probably start with a simple test light. There are a limited number of circuits that you wouldn't want to use a test light but they are mostly computer (PCM) and gauge related (oh, and one big one - the airbag - never use a test light on the airbag circuit). Other than that, a test light can be an extremely useful and easy-to-use diagnostic tool.
Most of the time you will be trying to determine whether power is available where it should be or whether a circuit has a good ground. Those are the two most basic issues you will experience with electrical problems. It's very simple to use a test light to determine those things.
For example, suppose you have a problem with your front turn signal. Turn your ignition and turn signal on. Use your test light at the front lamp to see if you get flashing power on the blue wire. If so, the problem is the socket or bulb. If not, move up the circuit to the DRL module behind the radio. Use your test light to test for flashing power on the blue wire there. If so, then you know you've got a break in the blue wire somewhere between there and the front lamp. If not, use your test light to check for flashing power at the blue with white stripe wire going into the DRL module. If so, you know the DRL module is the problem (power is going in but not coming out). If not, move up the circuit to the turn signal switch wires at the base of the steering column... you get the idea.
I always start with a test light before getting out my multimeter. In fact, I use one so often that it was worth it for me to buy the advanced Power Probe III test light that sells for about $100. But you can get a basic test light for under $10.
There's good information about test lights here: http://www.bcae1.com/testlite.htm
The same site also has good information on multimeters: http://www.bcae1.com/vomillia.htm
You should probably start with a simple test light. There are a limited number of circuits that you wouldn't want to use a test light but they are mostly computer (PCM) and gauge related (oh, and one big one - the airbag - never use a test light on the airbag circuit). Other than that, a test light can be an extremely useful and easy-to-use diagnostic tool.
Most of the time you will be trying to determine whether power is available where it should be or whether a circuit has a good ground. Those are the two most basic issues you will experience with electrical problems. It's very simple to use a test light to determine those things.
For example, suppose you have a problem with your front turn signal. Turn your ignition and turn signal on. Use your test light at the front lamp to see if you get flashing power on the blue wire. If so, the problem is the socket or bulb. If not, move up the circuit to the DRL module behind the radio. Use your test light to test for flashing power on the blue wire there. If so, then you know you've got a break in the blue wire somewhere between there and the front lamp. If not, use your test light to check for flashing power at the blue with white stripe wire going into the DRL module. If so, you know the DRL module is the problem (power is going in but not coming out). If not, move up the circuit to the turn signal switch wires at the base of the steering column... you get the idea.
I always start with a test light before getting out my multimeter. In fact, I use one so often that it was worth it for me to buy the advanced Power Probe III test light that sells for about $100. But you can get a basic test light for under $10.
There's good information about test lights here: http://www.bcae1.com/testlite.htm
The same site also has good information on multimeters: http://www.bcae1.com/vomillia.htm
08-07-2012, 08:03 PM
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Continuity test is a mode on a multimeter to make it act like a simple test light. Usually it makes a tone if there is a conductive path between the two leads. No tone = fault in the path.
A continuity tester works whether there is a live source voltage from the car or not, because the meter will apply a signal of it's own. Most test lights that I have seen don't have their own power/signal source, the bulb only lights up if the car is providing power over the systems wires. WB's fancy $100 test light probably is more sophisticated.
A continuity tester works whether there is a live source voltage from the car or not, because the meter will apply a signal of it's own. Most test lights that I have seen don't have their own power/signal source, the bulb only lights up if the car is providing power over the systems wires. WB's fancy $100 test light probably is more sophisticated.
Last edited by Capricio; 08-07-2012 at 08:09 PM.
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08-07-2012, 11:23 PM
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Actually, I should clarify. Test light is good for ensuring there is a difference in potential (voltage) between something and ground... basically making sure you aren't grounded out.
Continuity tester is good for verifying a wire or conductor path isn't broken. They are also useful for identifying ends of wires or terminals where you can see where they go in, but don't know which conductor in a bundle they are where they come out.
Continuity tester is good for verifying a wire or conductor path isn't broken. They are also useful for identifying ends of wires or terminals where you can see where they go in, but don't know which conductor in a bundle they are where they come out.
08-08-2012, 07:42 AM
#10
If you're interested, you should check it out. I saw it advertised on Horsepower TV one weekend on Spike and just had to get one. It has 20' leads that clip to the car battery terminals so that, in addition to normal testing, you can power up or ground a circuit with a thumb switch on the tester. It's called the Power Probe III and you can find it on Amazon.
08-08-2012, 07:56 AM
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All I'm trying to figure out currently is if there is a broken or grounded out wire on my '04 Grand Cherokee with their notorious power window/door lock problem. I'm also trying to do the same to see why my subwoofer stopped working and my amp stays in protect mode in my Camaro. What would work best just to try to find those problems?
08-08-2012, 10:15 AM
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It's less a matter of the tool, than the mindset. A 4-1/2
digit DMM and a dome light bulb with leads can tell you
the same thing if you're chasing an open circuit. If you
need details like an exact TPS voltage then you need
the precision. But for continuity you're looking at the
current loop and if you know what -should- make the
light bulb light up (like a hot feed would light against
ground but not B+, a ground feed lights against B+
but not GND, an open will light ahainst neither) you
can get what you need, and for the price of scrap.
Of course good-enough DMMs are $3.99 at Harbor
Freight every day and not much more than that at
Wal-Mart. But an automotive light bulb will not burn
out its odd-sized internal fuse when you hook it up
in 10A current mode across the rails.
digit DMM and a dome light bulb with leads can tell you
the same thing if you're chasing an open circuit. If you
need details like an exact TPS voltage then you need
the precision. But for continuity you're looking at the
current loop and if you know what -should- make the
light bulb light up (like a hot feed would light against
ground but not B+, a ground feed lights against B+
but not GND, an open will light ahainst neither) you
can get what you need, and for the price of scrap.
Of course good-enough DMMs are $3.99 at Harbor
Freight every day and not much more than that at
Wal-Mart. But an automotive light bulb will not burn
out its odd-sized internal fuse when you hook it up
in 10A current mode across the rails.
08-08-2012, 12:53 PM
#13
All I'm trying to figure out currently is if there is a broken or grounded out wire on my '04 Grand Cherokee with their notorious power window/door lock problem. I'm also trying to do the same to see why my subwoofer stopped working and my amp stays in protect mode in my Camaro. What would work best just to try to find those problems?
Your audio system doesn't lend itself to testing with basic equipment either. Most often when an amp goes into protection mode, it's caused by a damaged speaker wire to the sub or a faulty sub. The protection light is caused by too much current flowing on the output side of the amp. A speaker wire shorting to ground can cause that and is easy to find - just follow the speaker wires looking for someplace where the insulation is damaged and the wire is touching metal. Or, you could just run a new speaker wire pair to the sub and see if the problem goes away. If that doesn't solve the problem then your sub is likely damaged. If you have a friend with a compatible amp, see if you can get the sub working with the other amp.
08-08-2012, 08:57 PM
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I am not very familiar with that Jeep problem but from what I've heard there is often a broken wire in the driver's door. You could get testing equipment such as a meter or test light but unless you know what each wire is supposed to do (i.e. you have a schematic), it will be difficult to isolate a problem. However, I've heard that this particular problem is usually easy to find - the broken wire will be quite visible inside the door. If you do have access to a schematic, post it here and we'll give you some tips on what to test.
Your audio system doesn't lend itself to testing with basic equipment either. Most often when an amp goes into protection mode, it's caused by a damaged speaker wire to the sub or a faulty sub. The protection light is caused by too much current flowing on the output side of the amp. A speaker wire shorting to ground can cause that and is easy to find - just follow the speaker wires looking for someplace where the insulation is damaged and the wire is touching metal. Or, you could just run a new speaker wire pair to the sub and see if the problem goes away. If that doesn't solve the problem then your sub is likely damaged. If you have a friend with a compatible amp, see if you can get the sub working with the other amp.
Your audio system doesn't lend itself to testing with basic equipment either. Most often when an amp goes into protection mode, it's caused by a damaged speaker wire to the sub or a faulty sub. The protection light is caused by too much current flowing on the output side of the amp. A speaker wire shorting to ground can cause that and is easy to find - just follow the speaker wires looking for someplace where the insulation is damaged and the wire is touching metal. Or, you could just run a new speaker wire pair to the sub and see if the problem goes away. If that doesn't solve the problem then your sub is likely damaged. If you have a friend with a compatible amp, see if you can get the sub working with the other amp.
In the Camaro I've already tried another amp and still no beans. I'll try to replace the wire going from the amp to the sub with a bigger gauge because I just used regular speaker wire. If that doesn't work I'll try to check and see if the sub itself is bad.
