private penguin

private penguin

Well-Known Member
Sorry - full of questions at the moment!

I'm looking to fit some lights to the roof bars. Worklights to the rear, spotlights on the front, and amber LED strobes for use at event sites etc. All in all it means quite a few wires to route up to the top.

Whats the best way to get them up and out there without causing a leaking hole in the bodywork? There isn't a snorkel (the easiest route). In my 300tdi the wires to the lights were already installed on purchase and went out through a gromit in the top corner above the rear door.
 
I got fed up trying to find a way to bring the wires for my roof lights into the cabin so I ran them down behind the rubber door seal on the pillar into the engine bay via the gutter on the wing and bought a wireless remote control unit for a fiver off E-Bay with a fob. This means I can switch them on and off remotely too.
 
Had a look today and found absolutely loads of space behind the trim panel to the sides of the windscreen... seems easy to gain access as well. Ran the first cable in today - a few to follow but need to cut and extend the cables first.
 
Thats the best place to run cables! Just be careful with the trim panel, its very easy to break off the tabs.
Mine has about 8 thick cables running up it, they powered the spot lights/roof beacon fitted by the first owner, now use them to power my dash cam!
Mark
 
Just trying to find some sort of thin flexible conduit to keep the cables tidy between the top of there and the roof rail (and probably along the inside edge of the roof rail as well)... thinking that black corrugated conduit stuff neatly cable tied to the rails should work well - just need to work out how to fix the bottom end where it meets that trim panel.
 
Just spoken to a friend who has suggested rather than running lots and lots of different cables up to the roof, I buy a length of 13 core trailer cable, merge all the wires into that in the engine bay and then split them off again on the roof so i'm only running one nice neat cable. Thoughts?
 
Best make sure you have the correct amperage wire available for what you are going to use .

Cheers
 
My only concern in that respect would be the front spots.

The LED stuff uses far less power than normal trailer light bulbs.

That said, I think i'm moving towards some form of LED bar for the front roof bar instead of the spots - and then probably put the spots on the radiator grille instead.
 
private penguin said:
The LED stuff uses far less power than normal trailer light bulbs.
Click to expand...
That's not really the case - a 100w led still draws 100w just like a 100w halogen - you just get a lot more light in that 100 watts!

I'm no sparky but I've seen some terrible wiring on LED light bars, work lights and spots, but people just tend to say "oh it'll be alright, its only an LED light" when they've wired in a 400w light bar, unfused, to a bit of pokey little speaker cable!

Even if you recycle some old but decent household flex you're better off than making do with thin cable that is going to melt and cause you grief or burning...
 
When you do run a cable for your roof bar, so many people will tell you quite rightly to consider carefully the current carrying capability of the cable you use. Then they use one good sized wire to feed two spots; OK and another good wire to feed the two floods; again OK. Then they run the whole shooting match back to ground on a single wire without considering Mr Kirchhoff's first law; the current flowing into a node (circuit) equals the current flowing out of the node. So the size of the ground wire should take that into account.
There is a small problem with advertising LEDs, some adverts quote the actual power and other adverts quote a figure which refers to the light output being equivalent to such and such a lamp. So read the small print carefully.
If you do resort to using something like a length of 13 way trailer cable then you must be prepared to double up or even treble up wires in the cable in order to carry the required current.
Circuits used in vehicle electrics are under quite a lot of environmental stress, so keeping out moisture must be a priority, silicone grease has uses here. The other place where vehicle electrics tend to fail is at connections where the slightest amount of tarnish can lead to heating within the joint ultimately leading to a failure or in the worst case destruction of the vehicle due to fire.
 
Saltlick said:
Er, Well yes, only 50w compared to 200w... :rolleyes:
Probably similar brightness etc.
Did you know that one wheel weighs a lot less than four wheels?!
Click to expand...

My point was that with LEDs you can generally get the same brightness for less wattage, therefore less current going through the cable. The key has to be to do the maths each time... obviously if you're installing a single light then its easy - look at the power rating on the box and make sure the cable is up to the job. I always try to allow a bit of a margin, even though the cable manufacturer will also have allowed a margin.

The first disco I bought had front driving lights on the bumper... wired in with domestic doorbell wire. The wiring had been done very simply - live connection straight off the battery, straight to the dashboard switch (no fuse), then to the lights in series, and finally back to the negative terminal on the battery. Needless to say when I discovered this i stopped using them until I had a chance to replace it all with a relay based system and some decent wire!
 
private penguin said:
The key has to be to do the maths each time... obviously if you're installing a single light then its easy - look at the power rating on the box and make sure the cable is up to the job. I always try to allow a bit of a margin, even though the cable manufacturer will also have allowed a margin.
Click to expand...


As easy as that what ever the kit is, but also include calculations voltage drop plus a bit for redundancy, and bobs your uncle. Simples
 
Thought I put up a couple of pics of my existing "roof" wiring. Dont know what the setup was intended to drive but the wiring is nice and robust, 3.5mm o/d, 1.5 CSA.
Mine doesn't have sunroofs, so the switches for the roof beacon and the aux plug in lights used the blank switch panel.
Thing to remember with automotive stuff is the power triangle, so 100 watts/12 volts = 8.3 Amps which is substantial.
I nabbed the 12 power socket from the rear cabin and mounted it in place of one of the aux switches, the wiring to the roof panel is always live, so its good for powering the dashcam.

 
Ta...Ill only take credit for the plug in socket, the rest was courtesy of Thames Water, who were the first owners!
 
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