Saturday, 29 December 2012

Fitting a Fog Light - Part 1


Well, I need to get a fog light fitted to VIN 10719 before she can pass the UK MOT. For it to pass the car needs a rear red "fog light" which can be turned on ONLY when the headlights are on, and must have an illuminated switch or other warning light to show the driver that they are active. Phew!

This is the progress so far. It's not all done, but I'll add to the post as it evolves. 

I've decided not to go down the temporarily light route. Better to have a permanent  working fog light in this country. You never know  when you might need it. Although I have no intention of using the car in bad weather you never know.

My original option was to do the modification outlined by the "how to" section on the deloreans.co.uk club site. However, this calls for a live feed to be soldered to the PCB board next to the inner brake light, thus illuminating it constantly when the fog light switch is used. However, VIN 10719 has one of the new PJGrady PCB's which have a common positive track to both the inner and outer lights. If I supplied power to this track BOTH brake lights would illuminate at all times, which would cancel out the braking indication. A certain fail for the MOT. So it was on to plan B.

The centre light section of my rear light cluster is open and without a reflector. My plan is to place a new bulb holder into the top or bottom third of this section which can be independently controlled by the fog light switch, thus not modifying the original PCB in any way and keeping all original functionality, while satisfying the MOT requirements.

To do this I first had to route wiring to carry the live feed for the lights. From the back passenger side  rear light cluster I ran a 17 amp red cable back behind the number plate holder and round into the left hand pontoon and out through the engine bay release handle. This required removal of the catalytic converter from the left hand side of the engine bay to allow me to reach up and along the pontoon and push the wire through the gap in the firewall. I then threaded it down and along the central console (remove the ash tray and rear tray to aid this) and out through one of the dummy switches. 

I needed to fit an illuminated 16 amp switch here, which would be fitted to the dummy switch, and draw an earth for it from the cigarette lighter so it would illuminate when powered up. Then I threaded another wire back from the switch, along the centre console, and out in the fuse box section behind the passenger seat. Here I could tap into the headlight relay live feed to allow the rear fog lights to only work when the headlights were on. This connection would also be fused with an in-line fuse holder.




All seemed ok. Walking to the back of the car I picked up the wire for the rear lights which had been dangling on the floor. As I did it touched the side of the car and "bang" sparks flew as power arced to earth. WTF! how can that happen? the key wasn't even in the ignition. 
After some investigation it turns out that the out of the two wires to the cigarette lighter the outer purple wire was the live, not the inner red wire. WTF again! Surely the red should always be live. That needs some further investigation, but some swapping of wires later all was working as it should. (the live for both the cigarette light and the element were wired into the holder, so both the purple and the red wires were LIVE)

Well, I say as it should, but the actual lights I'd rigged up on the rear array were not as good as I hopped. To act as a fog light they have to glow a fair bit, and the two three-LED units I got for £5 (a bargain I thought at the time) just don't give out enough light.

The fix. Well I need a better set of lights and all should be good. I have a couple of ideas and will post an update soon on how this all turns out.

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