Best way to learn how to do vehicle electrics

Wiring, instruments, switchgear etc

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Best way to learn how to do vehicle electrics

Postby Joose on Mon Apr 19, 2010 1:42 pm

Hi All,

Soon I am going to start doing the electrics on my car. I have to do the whole system from scratch and I am a bit daunted as to where to start! Is there a book or an internet site anyone can recommend for learning? I really dont know much about electrics and so I need some help for a dummy! :)
Building: 4AGE 20v Locost SA
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Re: Best way to learn how to do vehicle electrics

Postby ross on Mon Apr 19, 2010 3:00 pm

The first car I wired was my cobra, for that I used the wiring diagrams in a Haynes manual for a mini (circa 1985ish). The wiring on older cars is much simpler than new cars. The one area on the Locost where I was completely stumped was the wiring for the engine management system. Fortunately, Andre' was able to sort me out in that area. I had a bit of a struggle with the Ford stalk switches but using the Sierra manual I was able to get them working. Then just consider each circuit as a separate entity and it's not so daunting. Assuming you're using the chassis as the earth, then just ensure that the -ve terminal on the battery is well connected to the chassis.
Best of Luck
Ross
Locost chassis with Toyota 20 valve blacktop and T50 box.
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Re: Best way to learn how to do vehicle electrics

Postby muller on Mon Apr 19, 2010 3:30 pm

When you get down to the basics wiring is not that complicated.

I did nit by breaking it down into layers and do 1 bit at a time to avoid confusions.

1st layer is the basic power wiring (battery/alternator/startor etc)
2nd layer is your normal electrics - lights, indicators, fuel pump etc - run some 8 core trailer wiring to the front and back of the car, its the cheapest and neatest way to do it.
3rd layer is your management
Anton

Race car 1: Birkin IRS 4AGE 20v (TLR class B - B10)
Race car 2: Birkin IRS 4AGE 20v (TLR Class B for SO - B20)
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Re: Best way to learn how to do vehicle electrics

Postby Joose on Tue Apr 20, 2010 8:36 am

Thanks guys. I will give it a bash. How do I know when I need things like Relays, resistors, etc And what should be fused and at what amps?
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Re: Best way to learn how to do vehicle electrics

Postby ross on Tue Apr 20, 2010 9:27 am

Use of relays depends on the current rating of the switches, some switches are rated high enough so you can switch directly to whatever it is needs switching. Personally, I prefer to use relays on just about everything and I use only Hella. As a guide though, you'd be looking at the lights; dip, main and side is 3 relays. Then horn, fan, starter circuit, is three more plus whatever the engine management needs, probably two. Then the flasher relay for the indicators. Fuse all those separately then fuses for instruments, panel lights. I'm sure people will say this is a bit OTT but, it doesn't cost much, nor do the relays and fuses add much weight, and it's safer than risking a switch burning out.
Cheers,
Ross
Locost chassis with Toyota 20 valve blacktop and T50 box.
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Re: Best way to learn how to do vehicle electrics

Postby muller on Tue Apr 20, 2010 11:57 am

Anything that draw significant power should go through a relay - head lights, starter, horn, fuel pump etc. Your management wiring diagram will also stipulate what needs to be run on relays from that side.

Fuses... well that depends on what you are wiring the car up for? Race car, road car etc. On my race car I have 2 fuses, one for the starter and the biggest fuse I could find for everything else. My wiring is obviously very basic and the fuse is literally there just to stop a dead short - last thing I need is say the fuse for the fuel pump blowing on the last lap because the pump is running a bit hot etc.

For a road car I'd go a bit further and fuse the various functions separately, but still try try and keep it to about 5 fuses max.

Try and wire it up so that the fuses are easily accessible - nothing worse than having to undo 10 bolts just to replace a 5c fuse.
Anton

Race car 1: Birkin IRS 4AGE 20v (TLR class B - B10)
Race car 2: Birkin IRS 4AGE 20v (TLR Class B for SO - B20)
Road car: erm.. who cares
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Re: Best way to learn how to do vehicle electrics

Postby ross on Tue Apr 20, 2010 1:34 pm

Agree totally with accessibility, undoing a few bolts wouldn't really be an issue but sometimes you have to be a frigging contortionist to get at fuses. :lol:
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Re: Best way to learn how to do vehicle electrics

Postby muller on Tue Apr 20, 2010 2:03 pm

ross wrote:Agree totally with accessibility, undoing a few bolts wouldn't really be an issue but sometimes you have to be a frigging contortionist to get at fuses. :lol:

Nifty solution we "borrowed" from Andre, is to make up a panel under the dash on the passenger side with a hinge, undo 2 nuts and the whole wiring panel flips down and you have access to fuses, relays etc
Anton

Race car 1: Birkin IRS 4AGE 20v (TLR class B - B10)
Race car 2: Birkin IRS 4AGE 20v (TLR Class B for SO - B20)
Road car: erm.. who cares
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Re: Best way to learn how to do vehicle electrics

Postby Ben on Wed Apr 21, 2010 6:45 am

Thanks for a useful and informative post - it has answered several of my questions. One more though - regarding chassis earth. Is it acceptable/good practice to just grab earth from the chassis wherever you need it, or should one run two wires to everything? Or is it a case of "it depends"? I can imagine that for something big, like a starter motor, you might want solid cables to and from the battery directly.

And how should one connect to the chassis - I was thinking of a few strategically placed riv-nuts as earthing points.

Last one, relays - can one get neat "relay boxes", or do most people just buy loose relays and wire them up on some sort of panel board?

Thanks
Ben
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Re: Best way to learn how to do vehicle electrics

Postby muller on Wed Apr 21, 2010 7:23 am

Just grab an earth wherever you need one from the chassis. The only exception I do to this is to run a dedicated earth wire for the dashboard. It makes adding gauges easy because the itself dash is not always earthed and some gauges are sensitive to voltage fluctuations (such as the rev counter)

Starter and alternator use their engine mounts as earths.

Just run one thick (welding cable is works great) earth strap from the battery negative terminal to the chassis and to the engine block.

Re relays, I don't bother with the boxes. Rivet the relays neatly onto your wiring panel and use crimping lugs to attach the wires.
Anton

Race car 1: Birkin IRS 4AGE 20v (TLR class B - B10)
Race car 2: Birkin IRS 4AGE 20v (TLR Class B for SO - B20)
Road car: erm.. who cares
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Re: Best way to learn how to do vehicle electrics

Postby Joose on Wed Apr 21, 2010 8:47 am

thanks for all the replies guys! this has really helped. I am fairly confident that I can tackle the basic electric systems now. ECU and instruments might be a different story though - that stuff looks very complicated. Will just have to muddle through when I get there i suppose.
Building: 4AGE 20v Locost SA
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Re: Best way to learn how to do vehicle electrics

Postby ross on Thu Apr 22, 2010 9:51 am

Andre's advice to me was to run a separate (clean) live and earth dedicated to the ECU. My battery is at the back so I ran cables along the chassis to the front of the car. My earth connection at the battery is a 10mm bolt; bolted through one of the gussets. Regarding relays, my advice is still use Hella.
Cheers,
Ross
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