Sylva Mojo Build Diary

High level brake light - August 2005

Having now passed the 5000 mile mark in the Mojo, I'm increasingly aware that quite a few drivers of other cars do tend to tailgate in traffic (I guess because the drivers feels they can see 'over' you in a 'little kit car'). I'm also aware that the hydraulic brake light switch isn't quite as sensitive as it could be. In an attempt to reduce the chances of being rear-ended, I decided on two relatively easy upgrades:

1- Fit a high level brake light. Jon, who has been unfortunate enough to suffer 2 recent rear end shunts in his Caterham, got me thinking about this. His most recent repair has included having a high level brake light fitted. Having also seen various other kits with these fitted, I decided to do likewise.

2- Fit a microswitch to detect movement of the brake pedal. This is the method used on pretty much every production car. So, I bought a microswitch for £1.19 from Maplin, with a plan to run it in parallel with the existing hydraulic switch to give an element of fail-safe.

High Level LED Brake Light

The only real option is to mount to the roll bar on the Mojo, as the rear bodywork does not have any flat surfaces. A quick search on the Westfield boardroom found a few pictures of some installations. Some used zip ties, and some were bolted to tapped holes in the roll bar. I was initially unsure about drilling the bar, but decided that a couple of 4mm holes were not going to make much difference in all reality, plus I didn't like the 'unfinished' look from using zip ties. I then called in to my local trade motor factors and picked up a 'Street Wize JS196 36 LED' brake light for under a tenner.

The 2 mounting legs initially had a fairly large flat plate designed to sit against the rear window in a 'normal' car. I trimmed these down as much as possible, and then used some wet and dry paper wrapped around a tube to form a curved profile on the 'feet' so that they would fit snugly up against the roll bar. I then carefully measured the mounting points, checked, double checked, and then centre punched, drilled and tapped the 2 holes.

To minimise the wiring, I considered earthing the light directly onto one of the mounting bolts for the LED, but decided that this could look messy. So, I ran both the live and earth wires along the underside of the roll bar and down to the nearside of the engine compartment. I covered the wire with black insulating tape to disguise it as best as possible. I conveniently had a spare earthing point on the chassis, and wired the live feed in to the multiplug in the wiring feeding the rear lights.

I'm really pleased with the end result. Let's hope it encourages the tailgaters to hang back a little...

UPDATE: The plastic mounting brackets both failed, and araldite failed to rescue them for more than a few weeks. I therefore set about fabricating some equivalents using aluminium T-section, which was carefully cut to shape and then bent around to give the impression of an expensive piece of bracketry!

Photo to follow

Brake Pedal Microswitch

I've now finally got around to fitting the brake pedal switch. The hydraulic switch has been getting noticeably worse in recent weeks, to the extent that only a fairly abrupt stop would cause the brake lights to come on (the high level brake light enables me to check fairly easily). With the handbrake needing adjustment for the upcoming MOT, I had the tunnel panels off and the ECU out anyway, so decided to use the opportunity to wire in the microswitch.

First job was to work out where and how to mount the switch. I'm using it in a Normally Open setup (the switch has 3 terminals to allow you to use it is NO or NC) such that with the brake pedal at rest, the circuit is open. Hence I need the brake pedal to move away from the switch. The obvious choice was to mount the switch to act on the pedal arm, but this would have to be on the driver side of the pedal, potentially getting in the way of my foot. I made a temporary bracket, fitting the switch fairly high up to contact the pedal arm just below the bias bar tube. A quick trial run showed that this should clear my size 10s.

I was concerned that the movement of the pedal arm would be insufficient to actuate the switch, given that it was relatively close to the pedal pivot, but this didn't seem to be a problem. There was also a very convenient place to mount the bracket, so I cut out a final version from some scrap aluminium.

The microswitch itself has 2 very small mounting holes for M3 bolts. I tapped these out to M4, so that I could just use 2 M4 stainless bolts to mount it to the bracket.

The bracket itself was mounted to the side flat of the angle section of the chassis that supports the right hand end of the clutch and brake pedal axle. Sounds complicated? Here is a picture:

The bracket is mounted to the side of the angle section in the bottom left of the picture. I fitted 2 rivnuts to the bracket and drilled 2 holes through the chassis plate to enable 2 bolts to secure the bracket.

Wiring was the next job. I used a piggyback connector to get an additional wire from the existing brake light circuit at the fusebox, and wired this to one of the terminals on the microswitch, a very convenient run of about 6 inches! I then ran an additional wire down the centre tunnel. I haven't gone to the trouble of re-doing all of the spiral wrap, so the new wire is just cable tied to the loom at regular intervals. I then used another piggyback connector onto the output from the original hydraulic pressure switch, maintaining the original switching circuit in parallel to the new one. Connecting the other end of this new wire to the microswitch enabled me to test the circuit, and all worked as expected, with the brake lights coming on with a very light touch of the brake pedal. That's more like it!