Third Brake Light Fitting Guide

Since upgrading to the clear rear light kit that was originally supplied with my kit, I was concerned by the lack of illumination when hitting the brake pedal.  A few friends were running a round third brake light, so followed suit and bought my own.

There is a bit of a debate on the lotus 7 club forum about fitting third brake lights, so though it would be a good idea to make a post of how I fitted mine, so others can follow (if necessary). Now for the disclaimer... This is just the way I thought was best for my requirements, and I'm not saying my way is the correct way, but the guide should help or give ideas to most third brake light installations.

 

There wasn't much to buy, but I've listed it below (with links):-

• FIA 51 LED Rain Light - £30 from Demon Tweeks
• High Level Brake Loom - £9 from Caterham Parts
• Some 2 core electrical cable
• Some various size and length heat shrink tubing
• Three packs of black Sugru

First part - installing the wiring loom

The first step is the remove the grommet on the inside of the offside rear wing.  Once the grommet is removed, gently pull through the connector block (there is just enough slack) and remove the indicator connector block from the main loom by lifting the black clip with a flathead screwdriver as pictured below.





Lift clip with a flathead screwdriver to remove indicator connector block from main loom

Now fit the two connector blocks from the high level loom provided by Caterham - there should only be only one way this fits together.  Then push the whole lot back through the hole in the body panel, and refit the rubber grommet. 



Connecting the high level brake light loom

I thought long and hard about how to neatly get the wiring loom up to the bottom of the roll bar, and the best solution I could find was to thread the cable up through a very small hole where the underside of the boot joins together.  I used a two core wire which I threaded up between the seam of the boot, as you can see in the picture below.


Two core wire threaded up through boot seam

As I've carpeted my boot, you'll see that the two core wire comes very neatly out behind the carpet and just at the start of the roll bar. 


Two core wire coming out behind the boot carpet

Then I cut the cable loom to length and ensured there was plenty of the two core wire pulled through the top to allow plenty of slack.  All the wires were soldered together protected with a couple of layers of heat shrink tubing.  I cable tied everything in place as you can see in the picture below.


Cable loom and two core wire joined, heat shrunk and cable tied into place

Whilst I was at it, I decided to cut down the excess of microphone wire that I had (as I have a stereo microphone mounted on the underside of one of the harness straps).  I threaded the microphone wire and two core cable through some 7.5mm heat shrink tubing, heated it (neatly) and tire wrapped it into place on the roll bar.

Two core cable and microphone wire heat shrunk and tie wrapped into place

I thought at this stage it'd be a good idea to test the light!  So I just put a connector block into place, wired everything together and crossed my fingers.


Light connected with connector block

It worked - and is extremely bright too.  As these lights are LED the polarity will make a difference, so if you wire the light up and it doesn't work it may just be due to the polarity being wrong, simply re-wire and re-test and it 'should' work.

Rain light being tested - check out how bright it is

Now how to fit the light onto the roll bar
A number of other Caterhams I've seen have this third light fitted to the roll bar, by way of a suitably sized rubber lined P clip.  The P clip fits around the roll bar and is tightened with an M4 bolt which fits directly into the rear of the light.

As OCD as I always am, this wasn't quite elegant enough for my liking, so I looked into some other mounting solutions and the best idea I could come up with was to fit a u-bolt that was covered in rubber.

I contacted a number of U-bolt manufacturers, but none of them wanted to make a u-bolt in M3 size.  The u-bolt needed to be M3 in size, as this is the correct size for the thread of the bolt to fit through the mounting eyes on the light.

Lee (my business partner) has a lathe and other gear for making things like this, so I popped over to his, cracked open a beer and let him get to work. (well not entirely, but it sounds good!)


Tiger beer - whilst I was hard at work

 We used a piece of aluminium tube as a template to work out the bend and tube length required.


Aluminium tube offered up to roll bar as a template for bespoke u-bolt

The aluminium template was then flattened and measured.  We needed 130mm of material with approximately 15mm threads on both ends.  Brass was used as this is soft enough to bend into shape, but still provides enough rigidity too.

130mm brass tubing ready for machining.

The brass was a little too thick for the M3 size required, so 15mm of each end was machined to 2.8mm in diameter.

Brass rod being machined to 2.8mm diameter

Lee then used one of his M3 dies to cut a .5 pitched thread into both ends of the brass rod.  We then tested the thread with an M3 nut and it was perfect.

.5 pitched M3 thread cut into brass rod, ready for bending

Lee then carefully bent the brass rod around a 60mm piece of nylon he had lying around, and then slipped on a piece of black rubber tubing and the u-bolt was finished ready for fitting. 

60mm u-bolt with black rubber tubing and M3 threads

These round rain lights are supplied with a ten degree angle on the rear profile, and for the fitting system fabricated above, this angle fouls the roll bar and makes the light slanted.  The next dilemma was then to reduce this profile so that the light fits correctly.  The solution was Sugru - it's a mouldable plastic which sticks to pretty much anything and hardens into a tough rubberised silicone.

I trimmed a small amount of the profile off the rear of the light using a sharp scalpel to flatten it as much as possible before applying the sugru.

Third brake light and sugru in packaging

Opening the Sugru packaging reveals the gummy substance which is ready for moulding.  I used three packs of the black Sugru.

Sugru packet opened

Once moulded into shape on the rear of the light, I pressed the light up against the roll bar so the profile of the Sugru is indented with the roll bar shape for a good fit.  It's not an extremely elegant solution, but it works extremely well as the Sugru is rubbery it creates a really good fit against the roll bar.  The positive is that the Sugru is hidden when the light is fitted, so I've not real problem with the aesthetics of this solution.


Third brake light with Sugru roll bar profile applied to rear

We then fitted the u-bolt and the light. The u-bolt fits extremely well around the cross of the roll bar, the rubber tubing helps in creating a very secure mount, that will also not scratch the roll bar if removed.

Caterham R500 with third brake light fitted

In the picture below you can see how well the third brake light illuminates in comparison to the (extremely poor) illumination of the clear lights - you can hardly see they are on which is pretty scary indeed.

Caterham R500 with third brake light illuminated

Overall I'm extremely happy with the neat finish of the u-bolt mount we made, but for ease I'd recommend others the rubber p clip mounting method (detailed above).