Monday, November 19, 2007

Broken Brakes

Lotus Elan brake light switch, wrongly demonstrated in exploded form. Do not copy!My brake light switch stopped working the other day. I tried to purchase a new one from Halfords, whose catalogue assured me they had a brake light switch for a 1974 Lotus Elan, so I ordered it in for collection two days later. Was it correct? Was it hell is like! It was the brake light switch for a modern Elan. Utterly useless to me.

Figures, I suppose. I half expected it to be incorrect, but my well represented lazy gene convinced me to order it anyway, since it beat a trip to Bishops Stortford... and it might be right.

The worst part is, no one at Halfords seems to actually bother to correct the catalogue. They just shrug and send the part back marked as "no longer required". NO! It's not "no longer required"... it's plain "wrong"! There is an option for "wrong" on the computer, but they all ignore it and send it back as "no longer required", so the catalogue managers have no inkling they're sending out the wrong bit. I'm sure it's a part they carry, as it is common to several cars from the 1970s/1980s/probably even early 1990s.

Anyway, I was about to trundle up the road to Bishops Stortford to a motorfactor and get the part there, when someone on told me they were easy enough to fix. Apparently they get corroded and dirty inside, but if you clip them apart and polish up the contacts they're good as new.

So I popped down to the garage, looked at where the switch was mounted on the back of the pedal box, disconnected the spades and the plastic switch screws straight out. Fantastic. You don't even need tools. I ran a wire between the spades with the ignition on, just to be sure the switch was the faulty part, and the brake lights lit. I took the switch home, dismantled it, could see immediately it needed a clean, so I set to work with some glass paper and ten minutes later it was back together again (as shown in the photo).

Now, those of you familiar with this particular type of switch are probably already saying "Ohhhh!" - yup, it didn't work. Had I actually thought about the mechanism, rather than half-guessing how the switch came apart (I couldn't actually see it properly, on account of the spring sending its various parts in five different directions across the living room floor) then I would've realised I was doing it wrong. But I didn't.

I should note this is also where you need a multimeter, something I am now asking for at Christmas! If I had a multimeter, I could've simply measured resistance across the terminals of the switch and realised what I only discovered when I got down to the garage and fitted the part, without leaving the fireside - namely, the way I had put the switch together meant it was permanently "on". The way I assembled it (as shown) just makes the spring press the contact plate permanently against the contacts, rendering the switch no more useful than a length of wire. Obvious, with the benefit of hindsight.

I walked the ten minute walk, up the hill back to the house, cursing the rain, my stupidity at not taking my precision screwdriver set with me and not actually considering carefully enough how the mechanism needs to work. When I got back to the house and took the switch to pieces again, looking with a more analytical eye everything became clear:

There is a little square peg on the internal end of the push-button of the switch, which is clearly supposed to marry to the little square hole in the brass contact plate of exactly the same size. The correct configuration is with the contact plate the other way around to the way it is in the photo, inside the casing of the switch, and on the other end of the spring with the spring going up between the contacts to rest against the clip-on plastic "top".

The tricky part is when you clip the whole unit back together again. The contact plate needs to pass the contacts, so that when the switch is sealed, the spring pushes the plate back on to the contacts, but not past them - this is a push-to-break switch, not a push-to-make. When you push the button in, the contact plate is forced up towards the clip-off end of the switch, away from the contacts it sits between, breaking the circuit.

When in position, it is permanently "pushed" by the end of the brake pedal lever. The act of pushing brake pedal removes the lever from the end of the switch, allowing it to extend and make the circuit, illuminating the brake lights.

It took me four attempts to put the switch back together so that it functioned correctly. I can't think of any easy way to do it. It's just a case of trying until you suceed through dumb luck! But it does go, eventually, with the correct blend of brute force and ignorance. And my brake lights work once more. Happy days!