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A hopefully complete guide to car wiring


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#1 cruiza

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Posted 10 May 2010 - 08:26 PM

Hi Guys and gals
Well this is it, First up a Disclaimer, I am not an Auto Electrican by trade.
What I do have is Telecom Trade and Advanced Trade Cert, back when it was a four year apprenticeship, I am a qualified Electrican, and 20+ years of doing all sorts of interesting stuff from designing power systems in hospitials and Nurse call systems to fire alarms and working at mine sites, industry to domestic wiring. Currently I look after complex power systems for radar and communication systems in the aviation industry. Oh and I have wired / re-wired a few cars. Oh and I have terible handwriting and cann't spell, get over it.

Now wiring cars and working on cars is usually done by qualified trades people, because the consequences of doing it wrong, can be expensive or worst case fatal. Now wiring cars is fairly easy when you know how and understand whats happening and how things work, but it is up to you to make sure you know what you are doing and wetheir you should be attempting any work on a car, don't try to blame me if you stuff it up or it doesn't work the way you want. This advice is to help you but I am not resonsible for what you do and do not do.

So take care, take your time and have fun, but remmeber death can be fatal and no one wants to be deceased and dead.

Now I was hoping to find some simple program that I could use to draw wiring diagrams but so far have not found any, if you know of any please let me know.

OK to start with use Personal Protective Equipment
Safety glasses when soldering
Always take your watch and rings off when working on car electrices


When using insulation tape do not stretch it, it is tempting to stretch it when wrapping wires etc so it looks nice and neat, however tape will over time contract back to normal lenght and unwrap itself, leaving gooey sticky mess behind, so loom up you wries neatly and wrap tape carefully around without stretching it and it will stay nice and neat.

When soldering apply heat to what you are soldering and solder to what you want to solder this is so solder will get good penitration and a good connection. Don't try to melt solder onto soldering iron and then flow into item being soldered

When running wirers always run too much and leave long tails that can be trimed off once cabling is all tidied away and correct lenght is known and even then leave wires slightly to long.

Always use a fuse

Always put a connector on unterminated wires

Never run wires thru or around sharp edges, use cromites

Work area needs to be kept clean and tidy and well lite

Mistakes can be very costly be sure, be doubly sure of what you are doing, then check again

OK I am working on some videos on the correct methods of solderiong and stripping wire in the mean time admire my artistic talents with some simple wiring diagrams and circuit explainations.

Now to explain if you look at car wiring one circuit at a time it is very simple.
You have a battery, negative terminal is connected to body of car, positive terminal is connected to starter motor and fuse box and from there to all the electrical components in the car and from the components back to the car body and thus to negative terminal of battery
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Looking at a relay the terminals at the bottom

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Edited by cruiza, 10 May 2010 - 08:30 PM.


#2 cruiza

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Posted 10 May 2010 - 08:46 PM

Ok post number two

The ignition circuit on a car, in simple terms power from battery to ignition switch to the Start circuit or the normal engine running circuit
Yes the ignition is made up of two circuits
When starting the car power goes to the starter solinoid which is a heavy duty relay to swtich current from the battery on to the starter motor, also power goes to the coil all 12 volts

now once car has started and running ignition switch is in left in normal on position and the starter is circuit is no longer energised.
Coil now recieves it power via a second circuit which has a resistor in it, called a ballest resistor, in some cases the coil will have an internal ballest, in the Torana there is a resistor wire, that is the wire from the ignition switch to the coil has a resistance to it such that the voltage at the coil is lower, from memory voltage at coil when car is running is about 9 volts, the idea is when starting the car have the full 12 volts to help with starting but once engine is running reduce it to 9 volts so as not to burn out the points.

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#3 cruiza

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Posted 10 May 2010 - 08:53 PM

Post number three

OK now the circuit is alway battery to component back to battery via the car body

now sometimes it is nice and simple and power goes battery to fuse box to switch to component to car body, This is positive switching for example the heater

sometimes it is easier to have power go to the component and then to the switch to car body, this is negative switching for example interior lights

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#4 Yella-5000

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Posted 15 May 2010 - 10:12 PM

Good stuff.

What about doing multiple positive power supplies without ending up with a birds nest? i.e. installing multiple relays, which our poor old beasts sadly lack.

#5 cruiza

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Posted 16 May 2010 - 07:43 AM

can do and will I am very busy with work at the moment so it won't happen overnight but it will happen, anyone near rocky want a car re wire-red so I can get some photos

#6 hutch

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Posted 16 May 2010 - 08:59 AM

Here's one i prepared earlier,its a control panel for a paddle boat,pity you cant see the wiring connections at the fuses better,it would give you an idea as to how to do it.
Every circuit is relay contolled from a dash panel in the wheel house,the top set of relays are 24 volt and control the Gardner engine
and transmission ie steering clutches and the lower set are for all the lights,generating plant ect.




#7 Kermit SLR

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Posted 16 May 2010 - 11:10 PM

Completely rewired my LH a while ago. Fitted a Commodore fuse/relay box under the bonnet. Also a new blade fuse box under the dash. The only relay the old girl had was one for the horn. Fitted LED lights where i could to minimize the current draw. (looks better too).
Mostly followed the original wiring diagram, but with modifications for all the relays and different take offs from the fuses.
All joints soldered and heat shrinked, used waterproof connectors for all the multi wire connections.
All good so far. No alt light glowing like i used to have :rockon:

#8 Yella-5000

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Posted 17 May 2010 - 06:12 AM

can do and will I am very busy with work at the moment so it won't happen overnight but it will happen, anyone near rocky want a car re wire-red so I can get some photos

No worries, know what that's like. Just when you get round to it, no pressure. I've been limited to basic maintenance for the last couple of years, or is it nearly three now?

#9 marko1au

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Posted 18 May 2010 - 08:03 PM

MODS sticky please

#10 ben23

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Posted 30 October 2014 - 10:19 PM

As an auto electrician I can say there is good advice here and its good to see people who arent auto sparkies but know what they are doing. Sure there are some things I'd do differently but fundamentally your methods are fine and thats all that matters.






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