Novice auto electrician

[Adrian]

Hi all, following on from Paul's earlier thread. I know very little about auto electric or even how to use a multimeter. So after the discussion which book is best for learning and what type of basic meter would you suggest?

 

Thanks Adrian

[JohnD]

For the multimeter https://www.google.co.uk/#q=multimeter&tbm=shop from less the £10 to more than £110.  A cheap one will do you very well. One that whistles/bleeps on 'continuity' testing is useful.

 

How to learn to use it - google for "how to use a multimeter" - there are dozens, for you to choose from.   One must suit you.

 

But use it, on your car.   Put a crocodile clip end on the black lead, so you can clip it to an earth (any bare metal on body, chassis or engine) and then use the probe end on the red wire to, er, probe about.   Think of electricity like water in a reservoir.  It's under pressure (Volts) and if allowed to can flow out (Amps) down pipes (wires and components) that may be wide or narrow (Resistance). You'll almost never use the Amps scale, but the Volts scale is very useful to see where the volts have got to, or not, and then the Resistance scale to find out why not.. That's where the "continuity" test position is useful as it will show if a component that should allow water electricity  to pass through wont', like a dud bulb (whihv is a poor example as a bulb that doesn't light up is obviously faulty, but I hope that helps you see the light(!)

 

Better example is a component that doesn't work (EG windscreen wiper).    With car switched on, but not necessarily engine running, are there Volts at the right terminal on the wiper motor?    If not, is there continuity between the battery and the terminal?  If not, then either the switch is faulty (you can test that isn the same way) or a connection has become disconnected.   Trace the Volts from battery to ignition switch to wiper switch to see where they disappear.  You'll soon find out!

 

Good luck!

JOhn

[Adrian]

Ahhh, you see, whilst educated and at lest used to understand the thermodynamics of metamorphism as a trained geologist that little blighter called electricity and cars has always been elusive until I try to delve into their mystical depths. I think it's one of those thing that until you have a go it is somewhat of a mystical skill.

 

I've learnt a great deal so far but as I wiggle wires and lights that were on suddenly go off I thought it best to delve into you're knowledge to do the right thing.

 

I suppose the critical element of earthing the whole thing is to prevent a literal shock whilst probing. All information is greatly received.

[Clive]

the only plac you will get a shock is from the HT circuits, ie plug leads or coil king lead. Otherwise there is only 12V which is harmless. 

 

I use a £5 meter off ebay, and had a few previously but they get lost/broken/left too long with a battery in (leaked) and it works perfectly well. Downside is that it doesn't beep on continuity, but I can live with that.

 

The settings I use are 20v, for checking voltages, one of the resistance settings for continuity, and I have used the amps/current when trying to chase a problem on a friends car when his battery kept going flat.

 

As john says a croc clip on the neg lead is helpful, sometimes on pos too. I bougt a pair of leads with croc clips for a quid from china....

[pageste]

I don't want to put a damper on all the above advice as you can do an awful lot of faulting with a meter or even just a 12v light up screwdriver. I will be the elf n safety bore here though, always be in a position to disconnect battery if your going to be moving / connecting wires up. My own 13/60 lost a large part of its wiring loom when the previous owner had problems with the wiper motor which resulted in the motor seizing and an under dash fire. A good manual is very handy and I also have a laminated wiring diagram to work from which is very useful. I have to say designing and fitting a decent fusebox to the Herald and converting it to an alternator were two of the most satisfying jobs I did on the rebuild. Get that meter and have a bash.

[Adrian]

Thanks chaps

[Casper]

 

 

I suppose the critical element of earthing the whole thing is to prevent a literal shock whilst probing.

No.  I think this is the big thing that causes people difficulty in understanding car electrics.  

What we refer to as an 'earth' in motor vehicle terms is, as John says, the chassis or body.  In motor vehicle electrics these big lumps of metal, attached together, are really a huge wire, completing the circuit from the wire connected to the component, through the component, then to 'earth' and back to the battery. 

Another thing that can cause problems is where the switch is:  Is it 'supply switched', so that the switch controls whether electricity is fed to the component (e.g. lights), or is it 'earth switched' when the component has an unswitched supply and the switch controls whether the electricity can reach 'earth' and back to the battery (e.g. wipers).  Sometimes the component itself has a switch, such as the distributor points.

 

Con 

[dougbgt6]

Adrian, one more thing, beware the GT6 fuse box! There are 3 fuses each held by a connector at either end. Each connector is in fact two bits of metal which aren't electrically attached to each other until you put the fuse in. On the back of the fuse box each connector has multiple wire connections. A common fault is when the fuse makes contact with both bits of metal at one end but only one at the other, leaving one set of wires unconnected, leading to bizarre and misleading symptoms. So, always check the fuses and fuse box connectors first!

 

Also the GT6 head lights don't have a fuse!  And, all the current for the head lights goes through the dashboard switch. A bit of a fire hazard really, additional fuses and relays are a good idea..