bexxxhill Posted May 2, 2023 Share Posted May 2, 2023 Bizarre one this; I did a pre-MOT check around the car, no problems - excellent. Took it to the MOT station and got a big fat fail due to off-side front lights. Turn side lights on - comes on no problem Turn on indicator - no problem Turn on headlights - side light/headlight no problem Turn on indicators with headlights - indicator goes out and headlight dimly flashes Now I am assuming that this is an earth fault that has raised its lovely head, but where to start? I've stripped it down and can see nothing obvious (it was a vague hope). So is it just a case of checking every connection, and earth point to see if there is something amiss? Has anyone also had similar? I have been told the red/white on the switch can cause a problem, but it does seem a long way from the lights themselves.Any help much appreciated.Cheers, Nick Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 2, 2023 Member Share Posted May 2, 2023 Do you have a multimeter?And the appropriate wiring diagram? Please send me a Private Message with your email address if you'd like a copy.Jonathan Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 2, 2023 Member Share Posted May 2, 2023 Yes, could be a false route to earth. One way of locating those is to remove bulbs until the strange behaviour stops occurring. Then investigate the circuit of the relevant bulb. Or remove all of the bulbs and then replace one by one and ditto.Does the left side all work fine with the indicators flashing at a typical rate?Do the hazard lights work OK with all of the indicators joining in?Are there any LED lamps anywhere?Jonathan Link to comment Share on other sites More sharing options...
jbcollier Posted May 3, 2023 Share Posted May 3, 2023 Congratulations, you have a constant problem. They are easy to find. It's intermittent problems that cause PERSD (post electrical repair syndrome disorder) . Run to your auto parts store and buy a test light with an incandescent bulb. LED test lights and digital multimeters can smell voltage through some of the worst connections imaginable. A test light with an incandescent bulb lightly loads the circuit and will find poor connections much easier. Judging by your description, there is a common ground point used by the headlight and turn signal that is poor/corroded. Whichever one is on, is using the other to find ground. When both are on, the lower impedence headlight (half-heartedly) wins the day. Link to comment Share on other sites More sharing options...
bexxxhill Posted May 4, 2023 Author Share Posted May 4, 2023 The near side lights all work fine. The off side are wired up using same colours as near side. I've been through the whole lot now with both a multi meter for continuity and with the bulb method to see if the circuit is good, which it seems to be. Hazards work with all indicators too. No LEDS in the loop at all. Nick Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted May 4, 2023 Member Share Posted May 4, 2023 But the fault remains?I'd start pulling bulbs.Jonathan Link to comment Share on other sites More sharing options...
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