Guest Chri5 Posted February 14, 2009 Share Posted February 14, 2009 Right, Ive trawled through and read up on using the 2 inner brake light to fog light conversion threads, and theres alot of them lol 1 way is using the relays and resistors and 1 uses JUST 2 diodes in suitable places. Both seem to give the same effect. I want to do this mod to my Aristo, but am unsure of which method to do it. Ive noticed some people say the diode only way isnt the correct way but then others have done it this way with no problems at all Obviously its a J spec car, if that makes a difference and I already have a +ve feed to the back of the car with a switch & fuse etc Any advice would be good, cheers Quote Link to comment Share on other sites More sharing options...
Paul Posted February 14, 2009 Share Posted February 14, 2009 Had two diodes on my UK spec (facelift rear lights) for years without problems. Others seemed to frown upon it at the time and prefered to use relays etc? Why make things more difficult than they need to be? Quote Link to comment Share on other sites More sharing options...
rich_supra Posted February 15, 2009 Share Posted February 15, 2009 i just stuck a red bulb in one of the reverse lights and ran a new switch wire. Quote Link to comment Share on other sites More sharing options...
Guest Chri5 Posted February 15, 2009 Share Posted February 15, 2009 Hmmm, well I may have to try the diode method Thats what Ive done first but it doesnt look anywhere near bright enough to pass as fog light Its with an 24 LED bulb too Quote Link to comment Share on other sites More sharing options...
MA70 Posted February 15, 2009 Share Posted February 15, 2009 Hi Chris, Neither way is incorrect, however my recommendation would be to use a relay if you are not familiar with diodes or circuit design. Using the wrong diodes, or connecting them incorrectly, will rapidly result in melted diodes and possible damage to the vehicle circuits feeding them. You are more likely to wire up the relay correctly. If you are using 21W incandesant lamps and are using a pair of diodes for each lamp, the diodes will need to be capable of carrying 2A continuously, with sufficient cooling to dissipate about 1.75W. If you are using a pair of diodes to feed both lamps the current and power ratings will need to double. I would opt for dual TO220 devices with insulated tabs so they could be fixed to some convienent metalwork for cooling. Using diodes will result in the lamps, fed from the diode, being slightly dimmer than thoes fed directly. This is due to the 0.8V – 1.0V lost across the diode. If you are using an LED array as a lamp, the current will probably be a lower, and it is possible you may be able to adjust the series resistor to counter the voltage drop of the diode. For your information I have used a relay. I’m not sure why you suggest resistors are needed with the relay though ! Hope that helps Mark Quote Link to comment Share on other sites More sharing options...
rich_supra Posted February 15, 2009 Share Posted February 15, 2009 re read replies Quote Link to comment Share on other sites More sharing options...
Pixelfill Posted February 15, 2009 Share Posted February 15, 2009 Hi Chris, Neither way is incorrect, however my recommendation would be to use a relay if you are not familiar with diodes or circuit design. Using the wrong diodes, or connecting them incorrectly, will rapidly result in melted diodes and possible damage to the vehicle circuits feeding them. You are more likely to wire up the relay correctly. If you are using 21W incandesant lamps and are using a pair of diodes for each lamp, the diodes will need to be capable of carrying 2A continuously, with sufficient cooling to dissipate about 1.75W. If you are using a pair of diodes to feed both lamps the current and power ratings will need to double. I would opt for dual TO220 devices with insulated tabs so they could be fixed to some convienent metalwork for cooling. Using diodes will result in the lamps, fed from the diode, being slightly dimmer than thoes fed directly. This is due to the 0.8V – 1.0V lost across the diode. If you are using an LED array as a lamp, the current will probably be a lower, and it is possible you may be able to adjust the series resistor to counter the voltage drop of the diode. For your information I have used a relay. I’m not sure why you suggest resistors are needed with the relay though ! Hope that helps Mark I suspect he's referring to the resistors needed to fool the bulb fail ECU when the fog circuit is in use. Mike Quote Link to comment Share on other sites More sharing options...
MA70 Posted February 15, 2009 Share Posted February 15, 2009 When I got my car the inner 21W lamps were wired as fog lights only. So either the bulb fail ECU has been frigged to work with one set of light or disabled. I shall investigate further.......... Thanks Mike Quote Link to comment Share on other sites More sharing options...
Guest Chri5 Posted February 16, 2009 Share Posted February 16, 2009 Thanks for the replies guys, and the info on the diode method Mark. I think after reading the 2 relay guide over a few times, Im now more familier with what needs doing so Ive sinced ordered the relays and resistors from Maplin, and will be doing it that way And yes, Mike was right about the resistors being used for the bulb failure light fix Quote Link to comment Share on other sites More sharing options...
Guest Chri5 Posted February 22, 2009 Share Posted February 22, 2009 (edited) Been doing this today for my Aristo, and it works, 1st time aswell and the bulb warning light stays out too Great guide Also, on the Aristo it can be pretty much all wired and connected up off of the car due to the loom disconnecting about 15cm from the bulb holders, so these can be removed with it Ignore the red bulb also, its now back to a standard reverse bulb A few pics..... Tail lights Tail & Fogs Fogs with brakes Brakes only I was thinking of mounting it all inside the boot lid but then decided it would be a bit tight with trying to get the boot trim panel over the top of it, and due to the boot being opened and closed it probably wouldnt do the relays alot of good so extended the necessary wires down the corner of the boot behind the trim panel Edited February 22, 2009 by Chri5 (see edit history) Quote Link to comment Share on other sites More sharing options...
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