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Mattzuki Just got MTs
Joined: 30 Oct 2007 Odometer: 282 Location: Kent
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Posted: Mon Oct 20, 2008 12:20 pm Post subject: How do I use a digital multimeter?
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OK, first off I confess to ignorance of all things to with car electrical circuits.
From my previous post you'll see that my headlights don't work on dipped beam, but I've got side lights and full beam. The indicators don't work either, but the lights work with the hazard warning switch. The fuses are fine (not sure about the switch relay), and my hunch is that the problem lies with the switch unit on the steering column.
I bought a digital multimeter, so I would be really grateful if someone could tell me how to use it, what settings, where to place the needles and what I should test in this case.
Many thanks,
Matt.
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callagas Articulating
Joined: 17 Oct 2007 Odometer: 760 Location: East Midlands
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Posted: Mon Oct 20, 2008 2:05 pm Post subject:
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Electric's!Ahhh
Try checking all your earths for your lights, remove earth wires for lights in engine bay, clean them up and where the bolt on to your body. Next, you want to do a continuity test for your wires (Check theres not a break in the wires) I dont no what setting this is on your multimeter tho. Have a look at what colour the wires are to your lights, you should be able to trace them back to your dash. Sorry i cant be of much help. But it may get you started! Daft sugestion, but if have you checked fuses? Good look. Mick
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cynic-al Mud Obsessed
Joined: 14 Nov 2006 Odometer: 6062 Location: scunthorpe
1989 Suzuki SJ
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Posted: Mon Oct 20, 2008 2:07 pm Post subject:
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the two settings you will need will be voltage and continuity.
Most likely voltage youu will need to set to 20v DC. This is how you will know if there is power at certain points of the circuit (power to a switch, from a switch etc). Where you put the probe depends what you are trying to test but generally you need one as a reference on +ve or 0ve on the battery and the other you probe at what you think is the problem.
The second setting, continuity, not all have this. Some have a diode setting that you can use, others you have to use resistance. It doesn't matter what you have it set to, all you are trying to prove is if a switch or connection is letting power through. Put your meter on one of the settings mentioned above and touch the probes together, you will see the display changes from something like -1 (no circuit) to a number, probably 0. This indicates that there is a circuit.
You don't really need to know anything else for what your doing.
__________________________________ I know enough to be dangerous. |
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StuartL Just got MTs
Joined: 19 Mar 2007 Odometer: 247 Location: Thatcham, Berkshire, UK
1994 Suzuki Vitara
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Posted: Mon Oct 20, 2008 2:34 pm Post subject:
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cynic-al wrote: | The second setting, continuity, not all have this. Some have a diode setting that you can use, others you have to use resistance. It doesn't matter what you have it set to, all you are trying to prove is if a switch or connection is letting power through. Put your meter on one of the settings mentioned above and touch the probes together, you will see the display changes from something like -1 (no circuit) to a number, probably 0. This indicates that there is a circuit. |
A lot of modern multimeters have a beeper setting that beeps when there's electrical continuity between the probes. Often the icon looks like a set of waves, the kind of icon you see near a picture of an ear for the hearing aid signs.
If you have this on your multimeter you can do very easy continuity tests by putting one of the probes at one end of the wire and the other touching the various components until it beeps.
Do be aware, as with all electrical work, that it's probably safer to disconnect the battery while you're doing it. You're unlikely to damage anything but it's not worth the risk. This does mean that you're reliant on wire continuity tests but if you suspect the switch the Haynes manual should give you a diagram of how the switch wiring should be done.
Don't connect the probes to a voltage while in continuity mode as you're likely to blow a fuse or component inside the multimeter. An example of what not to do is set your multimeter to 'resistance' or 'continuity' and then putting the probes across the battery. Good multimeters will glare at you and sulk in the corner. Bad multimeters won't work again.
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Mattzuki Just got MTs
Joined: 30 Oct 2007 Odometer: 282 Location: Kent
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Posted: Mon Oct 20, 2008 2:49 pm Post subject:
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cheers so far guys.
The earths are all good, I did them all a while back (no harm double checking I suppose though)
If I pull the plug at the back of the headlight switch can I test the circuits by putting the probes into the connectors? Would that be on the DC setting?
cheers,
Matt
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belmont_man Just got MTs
Joined: 26 Oct 2004 Odometer: 106 Location: SW London
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Posted: Mon Oct 20, 2008 3:03 pm Post subject:
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basically a meter has 2 wires one red one black.
if it is a digital metere witha lcd display it does not matter which way around you connect the wires.
usually it is red to positive , black to the earth also called negative, or the side connected to the chassi and car metal work.
to test the lights first check the bulbs.
when people mention continuity they are just saying put it on resistance setting, join the two probes together and the reading should go to zero, now put them on the bulb and they should do the same if the filoment is okay.
now put the setting on 20 volts.
and connect the probe ends to the battery, it should read 12 -13.5 volts.
then connect the red to the + and the black probe to to any chassi metal work you might have to scratch through the paint. it should read 12 volts again.
then go back to the bulb connector
one of these should be connected to the chassi at all times assuming normal wiring.
if it will reach you can keep the red on + battery and the black poke it in the bulb conectors, you should read 12 volts when it finds the earth connection.
it should be the same terminal both sides. if you do not get 12 volts then you either have not found earth or it is not connected.
if as you say both sides have the same fault it is likely to be the source of the 12 volts supply at fault.
if you can get to the back of the switch you can check with all the wires disconnected thet switch actually connects and disconnects the terminals on the back when you operate the switch.
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back at the bulb holder
connect one probe to the earth connection you found earlier, still on 20 volt setting, with the lights on you should get 12 volts in one of the other terminal. switch to high / low beam and you should get 12v in the remaining terminal.
I hope this points you in the right direction as a begineer.
John
__________________________________ vitar swb
I use "Obtainium": any material at hand that will fit. |
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belmont_man Just got MTs
Joined: 26 Oct 2004 Odometer: 106 Location: SW London
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Posted: Mon Oct 20, 2008 3:04 pm Post subject:
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dc is direct current as in normal car batterys, ac is only found on mains or on the back of alternators.
use DC setting
__________________________________ vitar swb
I use "Obtainium": any material at hand that will fit. |
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:) Mud Obsessed
Joined: 06 Feb 2006 Odometer: 4337 Location: Norfolk
1995 Land Rover Defender
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Posted: Mon Oct 20, 2008 3:29 pm Post subject:
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A while back I did a guide for someone else on the forum ... HERE.
Unfortunately the picture of the meter has gone, but maybe the rest of the explanation is still understandable?
--
Tim.
__________________________________ -- Timothy Birt -- |
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Mattzuki Just got MTs
Joined: 30 Oct 2007 Odometer: 282 Location: Kent
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Posted: Mon Oct 20, 2008 6:04 pm Post subject:
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Thanks everybody, I think there's enough to go on. Tim - your link is very useful thanks.
Matt
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