What grade of wire cable?

Post by **tingo** » Thu Apr 23, 2009 8:06 pm

Hi all,

I need to replace the black earth wire which returns from a headlamp. It has been bodged by a previous owner and has all sorts of connectors and sticky tape holding it together. Every couple of months something shakes loose and I am fed up of having to prod around in the dark to get a connection.

What standard of wire should it be? Can I just go into a shop and ask for headlamp wire or do I need a morris supplier? I've got a reel of house lighting wire lying around - would that be a bad thing to fit given that the circuit has a fuse?

Thanks.

Post by **mike.perry** » Thu Apr 23, 2009 8:27 pm

According to my Autosparks catalogue, for headlight wiring you need a 28/0.3 cable which will carry 17amps. As it is an earth cable it should be black. You should be able to buy it in any motor accessory/electrical shop. Ensure that the cable is securely earthed.
If the earth cable is botched, what is the rest of the wiring like. It may be wise to fit a new loom before you have an electrical fire.

Post by **tingo** » Thu Apr 23, 2009 8:46 pm

Thanks Mike. The rest of the wiring looks ok, except that some of it has caught overspray from undersealing and is a bit sticky in places. I don't think underseal should damage it though should it?

Post by **PAULJ** » Thu Apr 23, 2009 8:51 pm

By my calculations 17 x 12=204 so a cable, capable of carrying 17amps at 12 volts would be excessive for a standard headlight. Im not disputing your book Mike im questioning my knowledge. Also as it is an earth it can be smaller as it does not carry the same load. I have just made my own loom for my resto so I hope Im kind of right

Post by **tingo** » Thu Apr 23, 2009 9:17 pm

Hi Paul
Do you have instructions (or a shopping list) for making your own loom? Presumably you have to buy about 8 reels of different coloured wires and cut them to set lengths? I don't really want to replace all the wiring yet as I don't think it's got to the fire risk stage and there are bigger jobs to do.

Post by **tingo** » Thu Apr 23, 2009 9:24 pm

I think I make it 26 reels of different colours

by looking at the wiring diagram in my Haynes manual!

Post by **paulk** » Thu Apr 23, 2009 9:25 pm

A company I've used ( http://www.vehicle-wiring-products.eu/V ... mepage.php )
They will sell you all the different colour combination wires by the Metre. (other wiring companies are available

)

Even the different trace colours are available.

Post by **PAULJ** » Thu Apr 23, 2009 9:53 pm

tingo, there is a very good diagram at the beginning of this section of the forum. I have made my own because I have customised my car with altinator, mini column switches, Two speed wipers, front and rear heated screens so for me it was the way ahead. If you don't know your way around the loom, and I don't wish to be patronising, you would be better buying a ready made loom. A standard Moggy is probably one of the simplest looms to fit. Ref your problem, you can buy a coil of black wire from Helfords. If you take your old piece with you and buy a bit that size you wont go far wrong. Wax oil will do no harm. If you use the household wire, again not a problem but that is cable not flex. Cable has a single copper strand whereas flex is more what you want like on a desk top lamp. This is just an opinion, I am not an auto electrician. Someone with far more knowledge than me will tell you otherwise. Bottom line is by the sound of it any thing will be better than the earth you have, and no bad earth will give you a fire.

Post by **tingo** » Thu Apr 23, 2009 9:56 pm

Thanks for the link PaulK. The website confirms Mike's spec for headlight wiring and gives the spec for all other types as well.
If I don't find any wire for sale at the Bristol Classic Car Show next weekend I will order from them.

Thanks for the info PaulJ. I'm a beginner on everything car related - so all tips welcome. I can fit a wire, but the loom is probably beyond me.

Post by **mike.perry** » Thu Apr 23, 2009 10:22 pm

I must admit that when I read the Autosparks spec I thought the gauge was a bit heavy but when you are giving out advise you have to go by the book. If you had followed my incorrect advise and fitted the wrong wire and burned your car out you would not have been very pleased with me.
Having said that I expect the gauge I gave you is capable of carrying the power of two headlights. The smaller gauge is 14/0.3 which will carry 8.75amp. Cable size = AMPS=WATTS/VOLTS
I have installed new looms in my cars which include all the accessories such as front & rear fogs, flashing indicators in the MM, reversing lights, boot light etc<br>

<br>

Post by **alex_holden** » Fri Apr 24, 2009 7:53 am

PAULJ wrote:Also as it is an earth it can be smaller as it does not carry the same load.

That's not right. The same current flows into and out of the headlight filament.

Post by **Alec** » Sat Apr 25, 2009 8:23 am

Hello alex,
correct, but the manufacturers do fit a smaller section earth cable to save fractions of a penny it seems. The volt drop over such a small length will be negligible but it would warm up a little more than the feed cable.
As far a lighting effectiveness goes every volt that can be applied to the filament makes fitting correctly sized cable, if you are doing a rewire, worthwhile and that includes the earth cable. Light output drops dramatically with loss of rated voltage.

Alec

Post by **bigginger** » Sat Apr 25, 2009 11:14 pm

PAULJ wrote: If you use the household wire, again not a problem but that is cable not flex. Cable has a single copper strand whereas flex is more what you want like on a desk top lamp. This is just an opinion, I am not an auto electrician. Someone with far more knowledge than me will tell you otherwise.

Not quite sure what's being said here, but avoid (at all costs) the "single copper strand" - it's not designed to move, and will break/fail in no time if used on a car.
a

Post by **PAULJ** » Mon Apr 27, 2009 6:44 pm

Not quite sure what's being said here, but avoid (at all costs) the "single copper strand" - it's not designed to move, and will break/fail in no time if used on a car.
a[/quote]

Thats kind of what I was saying, When he sait household cable I was mearly pointing out the two types, not telling him to use it. As a last resort flex Not cable could be used

Post by **tingo** » Mon Apr 27, 2009 7:17 pm

I won't be using any last resorts. Now I know what grade of wire I need, I'm going to splash out 84p for the proper stuff! I'm hoping to pick some up at a show rather than pay £6 delivery.

Thanks for all the advice.

Post by **bigginger** » Mon Apr 27, 2009 7:34 pm

PAULJ wrote:Not quite sure what's being said here, but avoid (at all costs) the "single copper strand" - it's not designed to move, and will break/fail in no time if used on a car.
a

Thats kind of what I was saying, When he sait household cable I was mearly pointing out the two types, not telling him to use it. As a last resort flex Not cable could be used[/quote]

Not an attack, honest, just an attempt at clarification. Just that I've always thought that a cable was a collection of wires, and couldn't make your point out.
a

Post by **PAULJ** » Tue Apr 28, 2009 8:06 pm

Thats ok bigginger, Household wire such as twin and earth is cable so I would say you are right as its three wires, but then so is flex which is well flexable, anyway the bloke is sorted now so alls well...