andymal Posted August 3, 2021 Share Posted August 3, 2021 I've just had an interesting MoT note. The fog light works on dipped beam but goes out on main beam. It is something I have not noticed before and a quick look has not identified anything (so more detailed investigation to follow). Has anyone else come across this or know what the likely cause is? It seems strange to have a fog light working on main beam as in real fog you should only be using dipped beam. Link to comment Share on other sites More sharing options...
SM25T Posted August 3, 2021 Share Posted August 3, 2021 That's the design. Same on tin tops !! Link to comment Share on other sites More sharing options...
SM25T Posted August 3, 2021 Share Posted August 3, 2021 Idiot MoT tester Link to comment Share on other sites More sharing options...
Area Representative gileshudson Posted August 3, 2021 Area Representative Share Posted August 3, 2021 "4.5.3. Switching Front and rear fog lamp switches may be combined or independent switches. The switch or switches must: - be secure - be able to be operated from the normal driving position - operate the fog lamps as intended Rear fog lamps may be combined with the rear position lamps. Front and rear fog lamps are permitted to operate independently of any other lamps or ignition systems. The function of a fog lamp must not be adversely affected by the operation of any other lamp." Maybe the tester is flagging it re the last line above that I've stuck in bold and italics above, as you could argue that your setup does just that? Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted August 3, 2021 Member Share Posted August 3, 2021 Yes, as above that's how it's wired at the factory. I once had a problem at an MoT inspection when neither I nor the inspector knew that and couldn't turn the fog light on.I haven't heard of a MoT failure caused by the normal operation once that's known, but can see the potential from that wording.Jonathan Link to comment Share on other sites More sharing options...
andymal Posted August 3, 2021 Author Share Posted August 3, 2021 Thanks for the replies. The failure note is that the lamp has been adversely affected by the operation of another lamp. I have contacted Caterham and am hoping that I can obtain a confirmation that the lamp is operating as intended. With any luck that should then satisfy the tester. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted August 3, 2021 Member Share Posted August 3, 2021 Good move.And thanks for sharing.JonathanPS: If this becomes a problem it's easy to rewire so that it comes on as desired. Link to comment Share on other sites More sharing options...
andymal Posted August 3, 2021 Author Share Posted August 3, 2021 Caterham has confirmed that it was designed to operate this way. The proof is in the wiring diagram which shows that the fused live for the fog lamp comes from the dipped beam circuit. If anyone else suffers a similar MoT failure and finds this in the archives, I have the email from Caterham and can forward it. Link to comment Share on other sites More sharing options...
Wrightpayne Posted August 3, 2021 Share Posted August 3, 2021 Why is it designed like that? Link to comment Share on other sites More sharing options...
SM25T Posted August 3, 2021 Share Posted August 3, 2021 You wouldn't use high beam headlights in thick fog. Many tintops were the same Link to comment Share on other sites More sharing options...
John Vine Posted August 4, 2021 Share Posted August 4, 2021 I'd question what is the intended meaning of "adversely".And I agree with those who say it's supposed to work that way!JV Link to comment Share on other sites More sharing options...
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