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Quick MOT question...


danthecapriman

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I've got the Mercury in for MOT tomorrow. I've just checked everything over just to be sure but ive found a weird anomaly!

 

This car has hidden headlights which are revealed when the headlight switch is turned on.

Obviously being American this car has had its lights converted to have a separate sidelight and indicator. Originally they were in the same shared sidelight/indicator unit. To be uk legal it now has a separate sidelight in the new RHD headlight unit (same as shitloads of other cars have).

All the lights work and they work independently from each other. However, if you switch on the sidelights only they turn on but are on behind the closed headlight door. Turn on the dip beams and the doors open revealing the headlight and sidelight!

 

It's passed 4 mots like this so far but should this pass or fail?

Obviously being a us car there is no way of having this any closer to uk legal than it is now.

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They're vacuum operated! When there's vacuum pressure from the engine or inside the reservoir tanks the doors are held closed unless the switch for the headlights is on.

The good thing is that if the vacuum system fails the doors will automatically default to open via a pair of springs.

 

To me as it is sounds like a fail as the sidelights, even though they do work are obscured by the headlight doors = fail?

It's been fine for the four years or so it's been here going through mots but I'm using a new tester now and I think it's been a bit of an 'at the testers discretion' type thing going on up to now!

Shall I disconnect the headlight door before the test? Or leave it and see what happens. If it fails then the doors are easy to disconnect and leave open if I tell the garage how.

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I should say, the tester I'm using now is a reasonable guy! I've used him for mot and repairs on other cars for a while and never had trouble.

This was just one of those weird situations where I looked at the car and thought 'that's odd!'. I'm tempted to leave it as is and see what happens.

I'm going to show him a few things on the car tomorrow morning just so he knows where they are as it's not obvious, like the horn button, full beam button, and hazard switch, so I might explain it to him then and see what he thinks, and how to disconnect the doors to get around the issue?

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Take it to Dolphin Engineering, near Lymington,  they understand!

 

My mate takes his 92 C4 Vette there, with amber front sidelites,

 

and red rear indicators,  it always passes.  :)

My rear indicators are still red. The lenses are anyway, they've got amber high intensity bulbs behind though so it still shines amber through the red lense.

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It'll be interesting to see what happens. I've no idea if it would be a fail or not. There's absolutely no alternatives for a fix either unless you start adding extra lights!

 

I'm going to leave it be I think, see what gets said. If it fails, I'll simply pull the vacuum hoses off the two actuators which will interrupt the vacuum circuit and make the doors default to the open position leaving the lights exposed all the time. Should be an easy pass that way.

Once the MOT is over I'll just push the vacuum hoses back on and carry on as normal until next year!

It's a stupid bit of the MOT if it does cause a fail, it's just this one type of car causing an anomaly, but easily worked around.

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Presumably there is an electrovalve of some sort in the vacuum line that takes a dipped beam signal and interrupts the vscuum and allows ambient air in to the diwnstream pipework, thus opening the lamp doors.

 

Would it not be possible to change the wiring such that the electrovalves are driven from the sidelamp circuit rather than the dip? That way not only is it no longer an issue for MOT, but it works properly on the road too.

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Presumably there is an electrovalve of some sort in the vacuum line that takes a dipped beam signal and interrupts the vscuum and allows ambient air in to the diwnstream pipework, thus opening the lamp doors.

Would it not be possible to change the wiring such that the electrovalves are driven from the sidelamp circuit rather than the dip? That way not only is it no longer an issue for MOT, but it works properly on the road too.

Could well be, once it's got a ticket this time I'll look into it as it'd certainly make things easier.

 

 

In the mean time, I've disconnected the two doors and cable tied them up out the way of the lights. There should be no issue today. Once it's back I'll just cut the ties and reconnect everything.

 

Fingers crossed!

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Yep just sort it, it's not worth the testers licence should however is in charge of mot standards this week appear at his door after he has passed it and say they want to retest it.

 

Incidentally if that does ever happen once the test has finished and you are out, you always have an urgent appointment elsewhere and absolutely can not wait

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Yep just sort it, it's not worth the testers licence should however is in charge of mot standards this week appear at his door after he has passed it and say they want to retest it.

Incidentally if that does ever happen once the test has finished and you are out, you always have an urgent appointment elsewhere and absolutely can not wait

Absolutely. That's why I wanted to do something about it as I had a good idea it'd be a fail as it was. Strangely it's never been an issue before on previous MOT's but that doesn't make it right. I don't want to get him in the shit or put him on the spot with pressure to pass it regardless.

 

The chances of getting stopped for a spot test when out and about are slim anyway given the amount of use it gets so I'll take my chances on that. It's a pretty minor issue anyway as it works fine if the headlights are on.

I'll ask him this exact question after he's finished with it and see what he reckons.

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Ask him nothing, he will remember next year and fail it.

He's a good bloke to be fair. He thinks I'm raving mad with the cars I bring him to do stuff on!

He's got a few stock cars in his workshop too, some serious cash has been spent on them by the looks so he's a proper petrol head too.

The only one he hasn't seen of mine yet is the Capri but I'll take that down to him too once it's ready. Don't think there'll be any issues with that though given the work that's going into it!

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He's got a few stock cars in his workshop too, some serious cash has been spent on them by the looks so he's a proper petrol head too.

 

The best type of people imho, the garage I use for testing is run by banger racers but they race in all sorts of different stuff as well, they are good guys, they are fair and are very happy to show their findings while the car is still on the ramp
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