Mark Gibson Posted July 23, 2012 Share Posted July 23, 2012 I posted on this point a while ago but can't find my original thread so apologies for the duplicate posting. When I put my foot on the brake the side light bulbs illuminate in the front headlamps and the numberplate light and rear side light bulbs come on. Believing there to be a problem with the rear light clusters I purchased 2 new clusters and plugged them in only to find that the problem is still occurring. So now I know that there is nothing wrong with the rear lights, does anyone have any ideas of where the problem may be? Any help would be appreciated Link to comment Share on other sites More sharing options...
Mark Gibson Posted July 23, 2012 Author Share Posted July 23, 2012 Ah, found my original posting here As the brand new rear light clusters didn't solve the problem then would appreciate any other diagnoses for the problem. Thanks. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 23, 2012 Member Share Posted July 23, 2012 1 Take out both the brake light bulbs: does it still happen? 2 Do you, or anyone else know if there any relays or control units involved in either circuit? Jonathan Link to comment Share on other sites More sharing options...
rj Posted July 23, 2012 Share Posted July 23, 2012 Dodgy earth. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 23, 2012 Member Share Posted July 23, 2012 Quoting RJ: Dodgy earth.I saw that suggested in the other thread. Where would that be to cause this effect? Thanks Jonathan Link to comment Share on other sites More sharing options...
John Alston Posted July 23, 2012 Share Posted July 23, 2012 This is almost certainly a bad earth on one or other of the rear light clusters. When you brake the extra power required by the brake lights will show up any weakness in the earth circuit and the current will take the path of least resistance to earth. In your case via the lighting circuit. You can get the same problems with the indicator circuit too and then you get flashing side lights etc. Run a new earth from the rear light clusters and this should clear the problem. Link to comment Share on other sites More sharing options...
AdeC Posted July 23, 2012 Share Posted July 23, 2012 It may sound stupid but have you got the stop/tail bulbs in the right way round? Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 23, 2012 Member Share Posted July 23, 2012 I still don't understand how an earth fault can do this. I do understand how the wrong sort of bulb, wrongly inserted two filament bulb or touching feed circuits in the wiring or a bulb holder or in a two filament bulb could. What happens when you take the brake light bulbs out? Jonathan Edited by - Jonathan Kay on 23 Jul 2012 19:01:36 Link to comment Share on other sites More sharing options...
Johnty Lyons Posted July 23, 2012 Share Posted July 23, 2012 A bad earth at rear will certainly cause it. The current can't get to earth so it flows back throught the other filament and goes to earth in reverse fashion at front earth point. Simple my man seen it many times. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 23, 2012 Member Share Posted July 23, 2012 Sorry to be dense. I'm with you all on the idea ofthe earth from the brake light bulb being missing. So the current through the brake light bulb then goes through all the side/tail light bulbs... which way? Current goes from earth (now at 12V less the loss in the brake light bulb) to feed? So why do the side/tail light bulbs see any PD? The feed side should be open circuit. Feed to earth? How does the current get from the earth side of the brake light bulb to the feed side of the side/tail lights? Thanks Jonathan Link to comment Share on other sites More sharing options...
charlie_pank Posted July 23, 2012 Share Posted July 23, 2012 The rear lights share an earth point. If that is a poor contact then the current flows from the brake switch to the brake bulb, then back the wrong way through the other lights to find earth somewhere else. I have also seen it before and fixed it by running a new earth from the lights. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 23, 2012 Member Share Posted July 23, 2012 Thanks. Do you think the current flows the wrong way through the adjacent tail light bulb (which shares the bad earth) but the right way through all the other tail/ side bulbs? That wouldn't require a low impedance connection from the feed side to earth (which I think should be high impedance). But the illumination of the bulbs should be dimmer than normal if that's the way it's working because you have the bulbs in series. Should still be diagnosable by removing one or both brake light bulbs. Jonathan Link to comment Share on other sites More sharing options...
Johnty Lyons Posted July 23, 2012 Share Posted July 23, 2012 Yes the feed side is open Cct but the phase side is commoned at output from sw So 12v pos from brake light switch goes to one contact on the twin filament rear bulb then to holder which we are saying has lost its earth connection so returns wrong way through sie light filament thence to side light Cct wiring and thence to front side lights where it finds it's earth Simple. JJ Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 23, 2012 Member Share Posted July 23, 2012 Thank you. In my trade we call this "Continuing Professional Development" Jonathan PS: Of course LEDs couldn't have this problem... Link to comment Share on other sites More sharing options...
Mark Gibson Posted July 24, 2012 Author Share Posted July 24, 2012 Thanks all - it certainly seems that the earth is the most likely cause of the problem. I will get this checked out. Mark Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 30, 2012 Member Share Posted July 30, 2012 ... and the answer was? Jonathan Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted August 16, 2012 Member Share Posted August 16, 2012 Was there a solution? Jonathan Link to comment Share on other sites More sharing options...
susser Posted August 17, 2012 Share Posted August 17, 2012 We're waiting,,,,,,,,, we can wait all day if neccessary,,,,,,,,,,,,,,,,,,,,,,,,, Link to comment Share on other sites More sharing options...
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