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24. Front Lights

The lights had been put on the back-burner until some feedback from Caterham had been received. When the first headlight was unpacked it was found to have a piece of masking tape across the glass with the words "Wrong Lense" written on it. Caterham apologised but confirmed there should be no issue with using the lamp.

The front lights have a reputation of being difficult to fit - the manual even says that it is the most difficult step in the build. This seems to be related to the difficulty in passing the wires from the light assembly down through a grommet in the headlamp stay and into the chassis via another grommet.Before beginning I wanted to thoroughly understand the actual wiring - it wasn't immediately clear how the wiring from the indicator pods couple into the wiring from the headlight. This is actually very simple. There are four wires from the headlight that need to pass down to the chassis. The indicator live wire makes a fifth (and ultimately the repeater live wire makes a sixth). The ground wire for the indicator light needs to travel upwards into the headlight bowl to be terminated with the headlight ground.

The above wiring requirements means that a T-junction needs to be formed with the wiring - one branch of the T is the headlight; the second is the indicator; the main branch of the T is the combined wiring heading down the headlamp stay and into the chassis.

Having established that, the components were dry-assembled in order to gain some understanding of how the wiring fits together with the mechanical components:

Trial Assembly : Green wire from indicator joins those from the headlight - black wire goes up into the headlight

The existing plastic sleeve around the headlight wires was removed and then IVA trim was added to the bottom edge of the indicator pod, and the rubber encased bulb holder was screwed onto the pod (drain hole and the bottom).

Next, the indicator wires were protected with a sleeve of braid from the back of the light unit to the rear of the pod. A piece of heat shrink was used to secure this - including the rubber housing at the back of the light unit. This completed one branch of the T junction.

The next branch of the T junction concerned the wires coming down from the headlight, and the black wire from the indicator pod which needed to be terminated inside the headlight bowl. A piece of heat shrink was passed upwards along all the headlight wires, through the stem until it appeared inside the bowl. The indicator black wire can then be fed upwards through the same heat shrink tube, and through the grommet in the bowl (passing first through the nut and washer on the stem).

Then finally a piece of heat shrink is passed up over all the headlight wires and the green indicator wire. It was sufficiently large to accommodate the wires, the braid containing the indicator wires and the heat shrink passing up the stem. The top section only of this heat shrink was then heated to seal the assembly - the remainder of the heat shrink was not heated so that the wires were free to move inside. This made threading through the headlamp stay much easier. But before doing that, the grommet was slid / rolled up the outside of the heat shrink. As the heat shrink containing the wires was fed into the headlamp stay, the grommet could then be pushed into position.

Completed assembly ready for fitting to the chassis

The chassis grommet was handled the same way : Once the headlamp stay was attached to the chassis and the heat shrink containing the wires was passed through the hole, the grommet was slid up the heat shrink and pushed into position from the inside of the chassis.

The final step was to load the crimped connector pins on the end of the headlamp wires into the connector block ready for connection to the main loom. The position and colours of the wires in the loom connector were recorded and mapped against those from the headlight. Whilst not an exact mapping, it was clear that the two green/white wires in the loom must be the indicator (and repeater) wires - which would map to the green wire from the indicator. The rest of the headlamp wires were an exact colour match with those in the connector block in the main loom - HOWEVER - subsequent testing showed there was a mistake:

The headlamp wires that control the dipped headlights and main beam were transposed somewhere - either in the headlamp or the main loom (I didn't try to trace which of these was wrong according to the wiring diagrams). So, I spent some time with a multimeter to identify which wires on the main loom operated which lights. The diagram below is shows the connector block on the main loom, looking at the pins, connector clip uppermost:

  1. Ground / Earth (Black)

  2. Dipped headlights (Blue / Red)

  3. Main beam headlights (Blue / White)

  4. Indicator / Repeater (Green / White)

  5. Indicator / Repeater (Green / White)

  6. Daylight Running lights (Red / White)

Once the pins were pushed into the correct connector block locations, the remaining long lengths of wires were looped back on themselves and then covered with heat shrink - which was subsequently shrunk to create an effective seal.

The Econoseal crimped connectors were then inserted into the connector body from behind. They need to be pushed in a horizontal orientation relative to the connector body, with the crimped surface facing down - an audible click should be heard indicating the connector is latched into position.

(Note that in the above image the Blue/White and Blue/Red wires are transposed as per the above description)

The battery was then connected, Master Switch installed and switched on. On flicking the headlight switch to the first position (Daylight Running or Sidelights) the left hand light worked - the right hand did not. On operating the indicator switch - neither of the indicators flashed.

A brief moment of thought and I realised that the indicators would not operate with the ignition switch off - so the Hazard switch was operated and success!

Thanks to the great support of the Caterham & Lotus 7 Club, I discovered the wiring colour code within the headlamp (originally marked "Wrong Lense") and traced the headlight problem. The red wire supplying power for the Sidelight/Daylight Running was poorly crimped and wrapped in insulation tape. This was repaired with a new crimp and heat shrink - a retest showed all the lights now worked correctly.

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