tweedandbriar

tweedandbriar

Active Member
Hi,

First off, I need to say I am pretty useless reading wiring diagrams, a bit of a blind spot, so bear with me! I am looking to wire in a Light bar, already fitted and good to go. I would 'like' to be able to have it work both independently to the main beam but also to come on with the main beam. But to be honest, given my inherent lack of electrical knowledge thats likely too much for me.

So, I will settle for it coming on with the main beam. Can someone please help me identify how I would wire in the relay to do this? I understand that going straight from the battery is not needed as it will pull little power so it can all go behind the dashboard?



Its a 1999 110 if that helps.

Thanks again!
 
Last edited:
put relay in engine bay(drivers side, bulkhead by brake servo.black grommets to get cable be hind dash)
It’s easier to get to if there is a problem.
Main feed can be fed back to the battery for the relay power

Wire the lights bar to relay with a switch to turn on/off. Take a feed from main beam & put on switch side, you can then leave switch on so both lights & bar operates or override(switch off) so only high beam works works.
 
Hicap phill said:
Look on the back of the ignition barrel there may be a live pin there. Just make sure you fuse it where you can get to it easy. You can also go off the starter motor
Click to expand...

When you say off the starter motor, do you mean from within the engine bay, or from the main fuse box in the cab....or somewhere else?
 
So.
Here is a wee lesson on auto electrics.

Two things to consider when connecting devices,
(1) the Voltage in this case is a constant. ie 12V
(2) The current (or amperage) is what we need to look at and understand.

A standard H4 headlamp bulb is 55/60W
Lets take the 60W
Volts x Amps = Watts or (in this case) 60 = 12V x 5A
So the bulb draws 5A on high beam and 4.58A on dip (55 = 12 x 4.58)

The cable that connects the bulb to the 12V supply (battery) needs to be able to carry the 5A without getting hot.
Typically the vehicle designer installed a wire that would safely carry twice the rated load, so a 10W wire is used to connect the bulbs.
All wires have a resistance and resistors when they get asked to carry more than their rated current (Amps) get hot.

To stop the wires from getting so hot that they set fire to the surrounding wires and ultimately the vehicle, they are 'fused'.
To much current (above its rated value) the fuse gets so hot that it burns away and cuts off the supply. It protects the circuit.
Fitting a 20A fuse on a 10A wire is therefore not advisable.

In the same way fitting a wire rated @ 10A to a lightbar that takes 15A is also not advisable.
The thicker the wire the lower the resistance and the greater the current it can take.
The wires to the starter motor can carry around 150A.
Wires to a winch can carry around 500A.
Jump leads are thick, for a reason

So, connecting your lightbar to an existing 12V supply needs some consideration.
Is the wire you are connecting to capable of safely carrying the current it needs for its existing function and the additional current needed to energise the new device (your light bar for example).

Using a relay is a great idea as relays simply switch a high current directly to a supply independantly of the 'switch' current.
The cable carrying that supply still needs to be safely able to carry the required current and to be fused so that it can't get hot enough to cause a fire.

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miktdish said:
So.
Here is a wee lesson on auto electrics....
Click to expand...

Thanks, thats really helpful and clarifies things for me - I am pretty good with all the mechanical stuff, but the electrics have always been my Achilles heel!

Just need to establish the best feed point now, and importantly, where it is. :rolleyes:
 
tweedandbriar said:
Just need to establish the best feed point now, and importantly, where it is. :rolleyes:
Click to expand...

It's one that is easily accesible and that can carry the additional amperage.

The battery connects directly to the starter motor.The alternator connects to the main fuses (in the engine bay) and to the battery.
A feed from the main fuse board connects to the back of the ignition switch.

A lot of people make their own feed using an aftermarket fuse board.
Like this ...

https://www.ebay.co.uk/itm/256478523838

You can also get relay boards

https://www.ebay.co.uk/itm/395541610907

Often these are fitted into the battery box (under the passenger seat) with a fused supply straight off the battery.
Like this.

https://www.ebay.co.uk/itm/156482977801

The cables are then run out of the batterybox, along the chassis, up past the heater and to wherever it's needed.
If you need a switch in the cabin you can come in the gromets behind the binnacle and then back out to the device (whatever).
 
miktdish said:
It's one that is easily accesible and that can carry the additional amperage.

The battery connects directly to the starter motor.The alternator connects to the main fuses (in the engine bay) and to the battery.
A feed from the main fuse board connects to the back of the ignition switch.

A lot of people make their own feed using an aftermarket fuse board.
Like this ...

https://www.ebay.co.uk/itm/256478523838

You can also get relay boards

https://www.ebay.co.uk/itm/395541610907

Often these are fitted into the battery box (under the passenger seat) with a fused supply straight off the battery.
Like this.

https://www.ebay.co.uk/itm/156482977801

The cables are then run out of the batterybox, along the chassis, up past the heater and to wherever it's needed.
If you need a switch in the cabin you can come in the gromets behind the binnacle and then back out to the device (whatever).
Click to expand...

Thanks really appreciated - you're a patient man!!! 🍻
 
tweedandbriar said:
I would 'like' to be able to have it work both independently to the main beam but also to come on with the main beam. But to be honest, given my inherent lack of electrical knowledge thats likely too much for me.
Click to expand...

What switch have you got?
If you buy the correct switch then this is easily done, so buy an On/Off/On switch of a suitable rating (not much as its only switching a relay) Loads available.

Then you can sort it first with the High beam then simple add some wires to make it switchable when you want/feel more confident :).

Are you armed with a decent crimping tool, crimps and some wire? (dont use all the same colour;)).
Oh and draw a wiring dia of what you Plan/have done incase you need to go back to it, if you are not happy with wiring in the first place.

If you draw out what you plan and post on here you will get the 👍/👎.

J
 
marjon said:
What switch have you got?
If you buy the correct switch then this is easily done, so buy an On/Off/On switch of a suitable rating (not much as its only switching a relay) Loads available.

Then you can sort it first with the High beam then simple add some wires to make it switchable when you want/feel more confident :).

Are you armed with a decent crimping tool, crimps and some wire? (dont use all the same colour;)).
Oh and draw a wiring dia of what you Plan/have done incase you need to go back to it, if you are not happy with wiring in the first place.

If you draw out what you plan and post on here you will get the 👍/👎.

J
Click to expand...

Thanks, yep, got an excellent crimper, need to source some wire (not sure best gauge, does it need to be higher if coming from battery directly to feed the new fuse box or relay).

Great idea re' posting a pic, I'll get on it asap!
 
tweedandbriar said:
Thanks, yep, got an excellent crimper, need to source some wire (not sure best gauge, does it need to be higher if coming from battery directly to feed the new fuse box or relay).

Great idea re' posting a pic, I'll get on it asap!
Click to expand...

Wiring the switch, which only supplies the relay don't carry much load/current so can be small (ish).
Supply to the relay and the actual lights will need to be big enough for the load/current.

Use the info posted by @miktdish to calculate it. but at a guess your LED will draw less than the main beam wire size. What size wire comes out of your light bar, if it has any? use that as a gauge.
Always go up a size if it falls in the middle of sizes and fuse as low as possible.

If all you are adding is the light bar the new fusebox (although very neat) is not really needed, if you plan on possibly adding other stuff then it would be good to do it. Then a decent size of wire to supply all possible additions would need to be a heavier gauge wire. But for only a light bar not sure its worth it.

Its simple and easy once you get the hang of keeping the smoke in, honest :).

J
 
@marjon I have a loom and have just got some waterproof connectors. So I am gathering the gauge of the wire with the loom is sufficient though it is a little smaller than what comes out of the light bar. But not by much... I did install a separate fuse box in my Disco 2 - but then I had other stuff going on - I might just stick with one inline fuse for the light bar for now. My main plan is to have a three-way rocker switch to facilitate the light bar being independent, on (its own), with full beam, off altogether so full beam separate. Small steps eh?
 
tweedandbriar said:
I have a loom and have just got some waterproof connectors. So I am gathering the gauge of the wire with the loom is sufficient though it is a little smaller than what comes out of the light bar. But not by much..
Click to expand...
What loom?
“But not by much” sounds like a great way to work things out 🤔.

J
 
Quality light bar will tell you how many amps it will draw, should also have the wire size stamped on the insulation of the supplied loom, along with relay, fuse holder and maybe switch aswell.
Some are really quite powerful and need a good size cable.
Joining an additional loom with the supplied loom using a smaller gauge wire is asking for trouble.
 
Can I suggest that the title is amended to something like Light bar Wiring or similar so that it comes p on a title search for posts?
 
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