Right. Lets carry this on.
How to use a multimeter properly. Lets start with the very very basics.
There are two basic types, digital and analogue.
Digital will give you a number on a screen, analogue will give you an indication on a needle. Analogue are harder to read when you are a novice, and easier to break. So we'll assume you haven't stumped up the cash to buy a silly expensive analogue, and you've gone and bought one for around the £10 mark.
The cheap ones are great for doing basic fault finding, but they DO have their limitations. Less accuracy, less features, and in certain circumstances they will give you completely false readings (for example, if you are looking for alternator interference).
So, your cheap DMM (digital multimeter) will look something like this:
So, what are you looking at? There's a dial, that selects different settings, and different holes for your test leads to go in. Ignore the blue socket bottom left for now, that is for measuring transistors, you don't need that and I cannot be bothered going into transistor theory at the moment cos it'll complicate things! (BUT, if you want or need to know, then drop me a PM).
So, the dial selects the setting you need, but what about the holes? Where do you plug your leads in? Lets start with the easy one, COM. That means "common". The black lead goes in there, and there it stays. It is your earth, your reference, your ground, whatever we are going to call it for a particular job.
The other two holes, in this case labelled "5A" and "V horseshoe mA". On this particular meter, it is obvious where the lead goes, because the setting in which you need to put it in the "5A" hole has the box drawn around it in red.
However, even if this were not the case, the writing is telling you:
Use the TOP hole to measure current upto 5A.
Use the middle hole to measure voltage (AC or DC), horseshoes (ok, resistance. Horseshoe is "Ohms", the measurement of resistance) or currents up to 2000mA.
Basically, if you are measuring anything other than current, use the middle hole.
So what do the dial settings mean?
"OFF" - set the dial to here and it means that the meter is, er, off.
The next set of readings are "V~" - this lot are measuring AC voltages.
On your car, you don't need this setting unless you are looking at alternator faults, but because you bought a cheap-ass meter, we're not going to use it for that."V~ 500" - this is for measuring alternating voltages UPTO 500v (we call it alternating current). AC (alternating current) is what comes out of your sockets at home, and the only place you will see it on your car is directly out of the alternator before the regulator.
"V~200" - Alternating current upto 200v.
"A-..." This group of settings is for measuring current. The different numbers are the maximum measurement you can make on that setting.
"5A" - this one in red is where you need to put the red lead in the top hole. It is for measuring current upto 5A.
"hFE" - this setting is for measuring transistors. Ignore it.
"er, triangle pointing at a line..?" This is for measuring diodes (a diode in it's basic form is a one way valve. Current can pass one way, but not the other).
"Horseshoes! (Ohms)" - This group of settings is for measuring resistance.
"V-..." this group of settings measures DC voltage (this is the one you will be using mostly on your car).
Right, that's wonderful, how the F do you use all these settings? Well, the important thing is to know where to put your leads. Put them in the wrong place, you can make things go bang (usually your meter!).
Lets start at the top again.
"Off" - put the meter in this mode. If anything happens, if it displays anything, makes noise, explodes, or if ANYTHING at all happens, take it back to the shop.
"V~" - Select this setting. So, reading voltages upto 500v or 200v? How the heck are you supposed to know what the reading will be until you have measured it? Well, it's rather simple. You should know what you are expecting to see in the first place. But if you DON'T know what to expect, start at the highest setting, and drop the settings if needed.
How do we use the AC setting? Well, here's a little exercise you can do. Please, PLEASE, FFS be careful doing this, and ONLY do it if you feel safe and confident doing it. Actually, best not to do it, cos if you fry yourself you will only come moaning to me later. So we are going to PRETEND we are doing, this, ok?
When you measure a voltage, you are actually measuring a voltage "potential", that is to say how many "volts" exist between two points. Think of your car battery... You know it's 12v. You know that it will deliver, push, give, whatever, 12v from the red to the black. Same with your house. You have 220v on your "line" (brown wire)... But that is only when referenced to earth or neutral, which is "0v" (0v is STILl a potential. It's zero potential, but it is really, really important you recognise that it is STILL a voltage, voltages can be +, -, or zero. Zero volts does NOT mean "nothing", and I will expain why in a moment).
Go to your fuse box, select the 500v setting, stick the red prong in any "line" (NOT "live", it's not called live, it's called line) - that's the brown - terminal. Stick the black in any "neutral" (blue) terminal. You'll see it display 220v or there abouts. Now, swap red and black positions. You will see, again, 220v, or there abouts. Why does it display the same number and not a negative value? Because it is AC. The direction of the voltage changes 50 times a second. AC is always given as a positive number, because it wouldn't make much sense to do otherwise.
That there is your AC setting covered. You are always measuring between two points. Do yourself a favour though, if you are reading this guide because you want to learn how to use a meter, don't go buggering about with mains voltages, ok? If you really need to, drop me a PM and I'll pick up the phone and have a proper chat with you.
Next setting once I've had my lunch...