I need some help! The previous owner of my Mk1, instead of putting on an additional fog light, turned the third boot lid brake light into the fog light. By putting a switch in one of the blanks to the left of the steering wheel and routing a wire out to the boot, where he cut the green cable leading to the third brake light and put the new fog switch wire to it.
So now I have a third brake light that only works when you switch the fog switch. After a bit a fumbling around in the loom in the boot I have found the other end of the green wire.
What I want to know is If I attach the green wire to the new cable can anyone see a problem with doing this? By my reaconing the third light will light when brake depressed and will light also when the fog switch is in the on position. Will there be a problem when both fog and brake are on??? Can anyone see a problem???
Yes you will have problems,why not nip the wire rejoin the brake light so that works as normal and reroute the fog lamp wire to the drivers side rear reversing light cluster???nip the wire to the reversing light and solder to the bulb side take out the clear bulb and replace with a red one back end still looks clean,your brake light works and you have a rear fog lamp,job done should take around 20 min at most.
I have converted my middle brake light in the same way but I inserted a diode in the brake circuit. It also works as a brake light but the diode stops the foglight feed from illuminating the other brake lights. Passed 4 MOTs with no comment.
If you go this route choose a 2 or 3A diode and of course connect it the correct way round[:D]
Sorry for resurrecting an ancient discussion, this is one of those subjects where searching doesn’t turn up descriptiveness. I have a couple of quick questions from somebody who doesn’t really do electrical stuff.
So far I’ve removed the old attached fog light and replaced the switch with an authentic one. I’d like to use the top centre brake light as the fog light, the wire is currently too short and the MOT has crept up on me.
I don’t have a wire gauge measure, does anybody know what will suffice?
Does the green wire to the brake light actually have to be cut and attached to the switch wire, can they just share the terminal?
Hello, As luck would have it I just fixed my fog light this weekend where a previous owner had done the centre brake light modification and it had stopped working. I personally wouldn’t use the centre brake light as it’s not a very bright bulb anyway and I always thought the wiring was a bit of a botch job (at least it was on my car) . I removed the diode etc. and routed the fog light feed to the drivers side reversing light, then fitted a red LED 21w bulb (link below) Just use a test meter to check which wire in the light cluster multi-plug feeds the reversing light and then push that connector out the block from the other side (there’s a little plastic tab that holds it in) then just slide your fog light feed into the connector block. This way there’s no cuts to wiring and by using a red LED bulb the reversing light lens still looks clear from the back of the car.
I’m unclear from your post as to whether you still have the wiring for the fog light under the dash (the relay & feeds etc) plus a wire running back to the boot left over from the old fog light? If you just want some wiring to extend the stuff that’s there then pop into Halfords and pick up a reel of 8 Amp cable - it specifies that it can be used for rear fog lights so should be fine
I’m definitely sticking to the centre light, I mulled over the pros and cons from the discussions I found and that was my favourite, reasons for another time perhaps.
That’s right, I wired the replacement switch in before removing the fog light so I could make sure I’d done it correctly.
Did you feed the wire through from the front yourself? I’d sooner replace the whole length and remove a point of failure if it’s not too onerous.
14-core 8 amp… that would be 14 AWG? I’m sure they leave out the specifications so you can’t compare prices. I hope that’s overkill, the diode in the instructions I found was 3 amp.
I checked the continuity of the fog wire front to back and re-used that, the reason I changed mine from the centre brake light to the reverse light was that mine was just too unreliable, it would blow the bulb and the fuse randomly sometimes through braking, sometimes when you switched the fog light on.
feeding a wire from front to back isn’t too onerous, I did it a while back for a stereo amp feed along the bottom edge of the tunnel under the passenger side carpet, then up under the parcel shelf in the corner to the rear, but I already have a hole cut where the roll bar is fitted.
Follow-up thanks. The centre brake light plug was some kind of rubber-sealed thing I’ve never seen before, so I gave up and went with the reverse-light replacement using the bulb you suggested. Silly not to if, as you say, it’s little more than attaching an existing wire.