taillight problems! Earth?

[minty93 0]

HI everyone!

Right my mk3 rear lights have been playing up again. the right indicator flashes way to fast indicting a problem. Sure enough the offside rear taillights aren't working. I replaced the bulbs, still doesn't work, checked and replaced all fuses, still nothing. I got my multimeter out and there is power going to it. When i push on the brakes however they do light up. I'm thinking now its a possible earthing problem. Where do these lights get earthed so i can clean it and check it? Or any ideas at all will be greatly appreciated!!

 

Cheers

[Dooby 0]

Very likely to be as you suspect.

 

When you tested for power, where did you put the probes?

 

I'm not familiar with the Cortina's rear light cluster, but on the Cortina-based kit car I have, the earths from all the lamps (inc the indicators and reverse) are joined together in the unit and are then fed by one single brown cable to an earthing point on the chassis. So, it seems a little strange that the brake light works but the others don't.

 

Are you sure the brake light comes on as bright as it usually does? And, when you try the tail lights, brake lights and brake lights separately, do any of the other lights comes on a wee bit too?

 

Look closely inside the bulb holder - give the metal insides where the bulb fits a good wire-brushing, and do the same to the actual bulbs themselves - you do know they 'earth' through through the bulb's 'cap' - the main round bit which has the two li'l securing pins on them?

 

Car leccy is weird stuff, as I've discovered to my cost. What often happens is that if one component develops a faulty or weak earth connection, then - when that item is switched on - it'll partially work whilst also making other things come partly on! What happens is that the current cannot get to earth, so instead makes its way through another connected component and then to earth - so both items get supplied.

 

I'd start by making sure the bulb holders and bulbs themselves are really clean. (You can then give them a smear of something like copper-grease to keep them from oxidising up again.)

[sheffieldcortinacentre 753]

mk3's earth through the mounting, usually its the bit of bodywork & washer/nut that aren't making good contact.

 

prefacelift also give probs due to the lense mounting screws holding the rev/ind unit to the houseing & thus earth them to unit if these aren't tight it can also give probs.

[minty93 0]

yeah its very strange! when i press the bracks, the lights that dont work go on full nrightness asy they should while braking, while the nearside taillights dont brighten up at all and stay the same brightness!! confused.com

[Dooby 0]

Ha ha! Definitely earth, then!

 

That's almost identical to the situation I had when I fitted (cheapo... :blush: ) NEW bulb holders to my new clusters.

 

In mine it was traced to a very poor quality assembly method inside the actual bulb holder of the brake light that wouldn't light. These bulb holders simply had the earth wire bared for a centimetre and it sat inside the plastic holder with the metal bulb holder sleeve being just pushed in to the plastic body to press against this bare wire! Needless to say, it made very poor contact...

 

I soldered all these earth wires to the sleeve bodies, and problem solved.

 

It's weird behaviour, but what basically happens is that the electricity will find a new path even tho' it isn't as easy as the old direct path to earth. So when the current gets to the filament but can't go through to earth, if it can it'll go through another connected filament of a different bulb and then to earth - result, the wrong bulbs light up.

 

The first time you come across this weirdness, you're convinced someone's mysteriously swapped your bulb wiring during the night!

 

Try the cluster's earthing as Sheffield says, and it's probably also worth removing each bulb and checking inside the holders. Clean everything up, and give it a coat of WD40, copper grease (which I've used to good effect) or similar to keep it all corrosion-free.

 

Also check how the bulb holders' earths are joined together (daisy-chained?) in the cluster and see if there's anything dodgy there

[sheffieldcortinacentre 753]

mk3's only have lives going in & earth directly to/through the unit.no earth wires.

[Dooby 0]

Is there a metal strip which connects all the bulb holder's earths together or anything like that?

 

(I don't know - I don't have a Mk3. Cough - or even a Cortina...)

[sheffieldcortinacentre 753]

no, like i keep saying they earth through the metal unit which the bulbs directly attach into which is then bolted to the car.

 

unlike the mk4/5 which have seperate boards & earth wires.

 

no offence but your replies are just confuseing the post.

[Dooby 0]

No offence taken.

 

 

 

 

 

But I'm very embarrassed... :blush: