rear fogs

[pjbsaab]

hi saabists.........
Can anyone tell me....... should my 93 aero conv, have two rear fog lights showing, or just one?
have changed bulb, passed first mot with only offside lit...... but all wiring in place for nearside, but no glow!

Cheers...

[sgould]

All cars only have one now.  It's said it's done to avoid confusion with brake lights.

The arrangement is different in different years.  But the newer 9-3 from 2003 on only has one wire connected, even if both are there.  And there may be some electrickery in the rear electrical centre which sends the current, but acts on computer bus signals.

If you have an earlier 9-3 the connection in the lamp holder may be physically cut.  It was in my old 2002 9-5.  A piece of the metal circuitry had been cut and bent out of the way.

[Baxlin]

I hardwired the nearside one to the offside one, which overcame any programming foibles.

Regarding the confusion with brake lights, i daresay this is an 'official' view, and not necessarily sgould's opinion, but  I have a couple of observations here. 

Firstly, it's very rare to see brake lights on constantly, which is how you'd see fog lights, and of course you see fog lights for miles, that's what they're designed for, after all.

Secondly, from a selfish personal point, if someone behind me takes my fog lights as brake lights, presumably they'll brake and not hit me!

Malcolm

[sgould]

It's not so much the confusion as the masking. 

When you travel with a couple of 5w taillights on all the time, adding a couple of 21w brake lights is noticeable.

If you travel with the tail and foglights on all the time, adding the brake lights to that makes them far less noticeable.  There's some quirk of perception that makes double the light output appear less than that.

As an experiment, put on the brakes and look at the brake lights.  Leave them on and then turn on the tail lights.  This will increase the light output by about 25%, but in most cases it will be virtually unnoticeable.

[Baxlin]

I take your point, Will, but I'm not saying use foglights all the time, I used the word constant, ie as opposed to intermittent/momentary, which is how brake lights illuminate.

But yes, there is masking, as you say.   

[ScarbSaab]

I take your point, Will, but I'm not saying use foglights all the time, I used the word constant, ie as opposed to intermittent/momentary, which is how brake lights illuminate.

Will's point is that the brightness of the fog lights masks the switching on of the brake lights, which are often in the same cluster. If cars have a single fog light you stand a much better chance of spotting the brake lights coming on, or interpreting the different side brightnesses as both fog light and brake lights.

[Max Headroom]

Masking - Another good reason to turn your fog lights off when somebody catches up with you when driving in fog 

[Guyver1]

Masking - Another good reason to turn your fog lights off when somebody catches up with you when driving in fog 

If the vehicle behind catches up with you, you have to turn your fog lights off by law

[Max Headroom]

Nobody ever does, though!

[pjbsaab]

I hardwired the nearside one to the offside one, which overcame any programming foibles.

Regarding the confusion with brake lights, i daresay this is an 'official' view, and not necessarily sgould's opinion, but  I have a couple of observations here. 

Firstly, it's very rare to see brake lights on constantly, which is how you'd see fog lights, and of course you see fog lights for miles, that's what they're designed for, after all.

Secondly, from a selfish personal point, if someone behind me takes my fog lights as brake lights, presumably they'll brake and not hit me!

Malcolm

Hi malc..... thanks for the post, regarding the hard wireing, can u tell me how u did it as I cant see the point of having a light in place ... but not working!!

[Baxlin]

Can't remember offhand, I'll have to have a look!

[welshwizard]

But the newer 9-3 from 2003 on only has one wire connected, even if both are there.  And there may be some electrickery in the rear electrical centre which sends the current, but acts on computer bus signals.

My 2003 9-3 SS Aero had both sides wired for fogs, but only one bulb - depending on the market.  I got so used to moving the bulb to meet whichever requirements applied (TuV, RDW or VOSA), and I ended up having more expertise in this department than Phoenix Saab in Wimbledon - this is why I go to a dealer further away for work on my car