Wiring small light bar for reversing

Wiring small light bar for reversing

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Peter-j8c3u

Original Poster:

110 posts

44 months

Wednesday 22nd June 2022
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I need to fit a 6” 36w light bar so I can reverse at night safely, I’m planning on using the original feed to the bulb as a trigger but need to find a 12v supply in the boot, what’s the best way to get it,connect into the fuse box?
If so, what’s the best way?

RUSSELLM

6,001 posts

261 months

Wednesday 22nd June 2022
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Are you adding to the reverse lamp or replacing it ?

Byker28i

74,508 posts

231 months

Thursday 23rd June 2022
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I put a reversing camera fed into my head unit. I think it was £8, shallow and fits into the number plate and works great with the light from the reversing bulb.

Because of the smoked covers, I've also fitted LED bulbs which are brighter

If you're running a 6" light, why not look at LED ones, which have a tiny wattage. 36W equivalent would be 3 for 4W on the LED tape lights and can be fitted in a bar, so could be run off the standard reversing light bulb?

Edited by Byker28i on Thursday 23 June 08:43

Byker28i

74,508 posts

231 months

Thursday 23rd June 2022
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Peter-j8c3u

Original Poster:

110 posts

44 months

Thursday 23rd June 2022
quotequote all
Byker28i said:
I’d be worrying about melting the back of the car biglaugh

Peter-j8c3u

Original Poster:

110 posts

44 months

Thursday 23rd June 2022
quotequote all
RUSSELLM said:
Are you adding to the reverse lamp or replacing it ?
Adding to it.

Peter-j8c3u

Original Poster:

110 posts

44 months

Thursday 23rd June 2022
quotequote all
If you're running a 6" light, why not look at LED ones, which have a tiny wattage. 36W equivalent would be 3 for 4W on the LED tape lights and can be fitted in a bar, so could be run off the standard reversing light bulb?

It’s actually a 30w 6x led, typical of the ones you get off amazon. I want to mount it right under the valance. I just wanted a 12v switched feed to connect to, I’ll have another look at the fuse box and see if there’s something I could piggyback off of.


RUSSELLM

6,001 posts

261 months

Thursday 23rd June 2022
quotequote all
My owners manual is saying there's a 20A fuse for the rear clusters, so 240W

The lights, all on, appear to draw 136W, so fuse wise, you'd be OK if you decide to piggy back.

So the only thing to factor in, is the wires and the switch. The individual positive for the reverse lamp, will be carrying 4.75A instead of it's usual 1.75A, same for the reverse switch.

The neutral for the cluster could potentially have 8.67A going through it, instead of 5.67A

You could have a look at the gauge of the cable they've used. If you're not sure, check the cable against something else in the car that would need to carry a similar/bigger load. Switch wise, hopefully somebody knows the part number, so you can look up the spec.

I expect you'll be alright using the existing wires. Worst case scenario, use them to fire a relay... Which is where Penelope comes in biggrin



Polly Grigora

11,209 posts

123 months

Thursday 23rd June 2022
quotequote all
Peter-j8c3u said:
I need to fit a 6” 36w light bar so I can reverse at night safely, I’m planning on using the original feed to the bulb as a trigger but need to find a 12v supply in the boot, what’s the best way to get it,connect into the fuse box?
If so, what’s the best way?
Hold on a minutesmilesmilesmile

Why not disconnect the original reverse light and connect the light bar to the disconnected cable

Byker28i

74,508 posts

231 months

Thursday 23rd June 2022
quotequote all
Polly Grigora said:
Peter-j8c3u said:
I need to fit a 6” 36w light bar so I can reverse at night safely, I’m planning on using the original feed to the bulb as a trigger but need to find a 12v supply in the boot, what’s the best way to get it,connect into the fuse box?
If so, what’s the best way?
Hold on a minutesmilesmilesmile

Why not disconnect the original reverse light and connect the light bar to the disconnected cable
MOT requirements?

I'm just trying to work out in what scenario you'd need extra light whilst reversing, thats switchable on and off.

Is this one specific dark location? Would it be easier to add a motion activated spotlight to the place?
I put one of these solar lights at the bottom of the garden so I can find the dog at night
https://www.screwfix.com/p/luceco-lexs40b40-01-out...

Peter-j8c3u

Original Poster:

110 posts

44 months

Thursday 23rd June 2022
quotequote all
All sorted now. I used the earth behind the fuel tank (it’s just accessible), soldered the trigger to the + of the reverse bulb wire and used a piggyback fuse for + feed to the light on the relay.
I did it because I have to reverse 25m up my drive and then turn 90° into my yard. It’s dodgy without a decent light because there’s a kerb to the left that would ruin the wheels. My other car is just as bad, it’s an Audi and they’ve got stupid thin reverse lights, I have to keep my foot on the brake pedal to light it up, good job it’s an auto.

Polly Grigora

11,209 posts

123 months

Thursday 23rd June 2022
quotequote all
Byker28i said:
Polly Grigora said:
Peter-j8c3u said:
I need to fit a 6” 36w light bar so I can reverse at night safely, I’m planning on using the original feed to the bulb as a trigger but need to find a 12v supply in the boot, what’s the best way to get it,connect into the fuse box?
If so, what’s the best way?
Hold on a minutesmilesmilesmile

Why not disconnect the original reverse light and connect the light bar to the disconnected cable
MOT requirements?
Connect back to standard?

Panamax

6,077 posts

48 months

Thursday 23rd June 2022
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As others have said, just use low current LED and save yourself a world of hassle.

Polly Grigora

11,209 posts

123 months

Thursday 23rd June 2022
quotequote all
RUSSELLM said:
My owners manual is saying there's a 20A fuse for the rear clusters, so 240W

The lights, all on, appear to draw 136W, so fuse wise, you'd be OK if you decide to piggy back.

So the only thing to factor in, is the wires and the switch. The individual positive for the reverse lamp, will be carrying 4.75A instead of it's usual 1.75A, same for the reverse switch.

The neutral for the cluster could potentially have 8.67A going through it, instead of 5.67A

You could have a look at the gauge of the cable they've used. If you're not sure, check the cable against something else in the car that would need to carry a similar/bigger load. Switch wise, hopefully somebody knows the part number, so you can look up the spec.

I expect you'll be alright using the existing wires. Worst case scenario, use them to fire a relay... Which is where Penelope comes in biggrin
Having read the above calculation

Was a relay needed?

RUSSELLM

6,001 posts

261 months

Thursday 23rd June 2022
quotequote all
As long as the cable gauge and switch contact ratings are OK, no need for a relay.

Regardless, on my own car, I'd have just piggybacked off the existing wires smile

gruffalo

7,848 posts

240 months

Friday 24th June 2022
quotequote all
RUSSELLM said:
As long as the cable gauge and switch contact ratings are OK, no need for a relay.

Regardless, on my own car, I'd have just piggybacked off the existing wires smile
The switch will be rated for two reversing lights so 42W+.

If you change the revere light bulb to LED you will be drawing about this much power, the switch will be fine as will the wiring so just piggy back the two. https://www.reconelectrical.co.uk/image/data/pdfs/...

The wiring is I seem to remember 1.5mm but certainly not smaller than 1mm.


Edited by gruffalo on Friday 24th June 08:22

Polly Grigora

11,209 posts

123 months

Friday 24th June 2022
quotequote all
Thin wall cable innit or innit not?