ntc Posted June 6, 2021 Report Share Posted June 6, 2021 Show me to prove your statement Quote Link to post Share on other sites
SpitFireSIX Posted June 6, 2021 Report Share Posted June 6, 2021 (edited) Hi ntc, Look at any car schematic for enlightenment. For your edification, The Ignition lamp is the only "bulb" on the whole car that does not have an earth. The inverse of every other car "Bulb". The only bulb that can flow current both directions. Has that helped? Cheers, Iain. PS. Indicator bulb in most cars is bipolar as well. Edited June 6, 2021 by SpitFireSIX Indicator bulb Quote Link to post Share on other sites
ntc Posted June 7, 2021 Report Share Posted June 7, 2021 17 hours ago, SpitFireSIX said: Hi ntc, Look at any car schematic for enlightenment. For your edification, The Ignition lamp is the only "bulb" on the whole car that does not have an earth. The inverse of every other car "Bulb". The only bulb that can flow current both directions. Has that helped? Cheers, Iain. PS. Indicator bulb in most cars is bipolar as well. Disconnect the three black wires that earth the speedo and see what happens Quote Link to post Share on other sites
Mk2 Chopper Posted June 7, 2021 Report Share Posted June 7, 2021 17 hours ago, SpitFireSIX said: Hi ntc, Look at any car schematic for enlightenment. For your edification, The Ignition lamp is the only "bulb" on the whole car that does not have an earth. The inverse of every other car "Bulb". The only bulb that can flow current both directions. Has that helped? Cheers, Iain. PS. Indicator bulb in most cars is bipolar as well. Surely the alternator provides the ground (earth) for the ignition light, when the ignition is turned on. Then when the alternator is charging there is 12v going to both sides of the bulb and therefore it goes out. With the indicator dash bulb, the earth changes to the opposite side as you switch them on either left or right, but there is still an earth, the flow of power does indeed go in a different direction through the dash bulb depending which way you indicate. Gareth Quote Link to post Share on other sites
Les Pettitt Posted June 7, 2021 Author Report Share Posted June 7, 2021 Sorry Guys, You have lost me a bit now. As expected, when I remove the fan belt and start the engine the ignition light stays on and the lights don't flicker. (that is cubby box, interior lights and headlights). If I reconnect the fan belt and start the engine the ignition light goes out but I get the flicker. Is there anything else I can do? Do we still think it is time for a new alternator? I have emailed the suppliers of the current alternator but not got a reply yet. Regards Les Quote Link to post Share on other sites
Mike C Posted June 7, 2021 Report Share Posted June 7, 2021 A desperate roll of the dice would be a big capacitor on the wires feeding the lights. Quote Link to post Share on other sites
RobH Posted June 7, 2021 Report Share Posted June 7, 2021 1 hour ago, Les Pettitt said: Sorry Guys, You have lost me a bit now Ignore the argument Les - that is a digression that doesn't help you. At this point there probably isn't anything more you can do unless you have a spare alternator to hand. Quote Link to post Share on other sites
Mk2 Chopper Posted June 7, 2021 Report Share Posted June 7, 2021 2 hours ago, Les Pettitt said: Sorry Guys, You have lost me a bit now. As expected, when I remove the fan belt and start the engine the ignition light stays on and the lights don't flicker. (that is cubby box, interior lights and headlights). If I reconnect the fan belt and start the engine the ignition light goes out but I get the flicker. Is there anything else I can do? Do we still think it is time for a new alternator? I have emailed the suppliers of the current alternator but not got a reply yet. Regards Les Can you connect a bulb direct to the battery (when it's being charged by the alternator) and see if that flickers? Just thought it would point to the alternator and not dodgy light circuits. Otherwise I'd agree have the alternator tested or substitute for a known good one. Gareth Quote Link to post Share on other sites
Les Pettitt Posted June 7, 2021 Author Report Share Posted June 7, 2021 Hi Gareth, Directly on the (brand new) battery both bulb and analogue meter were steady as far as I could tell but I am a bit blinded now. Bulb was still pulsing when put on fuse box connection from alternator. What can we deduce from that? The pulsing is on cubby box light, interior lights and headlights which surely must all have different earths. Thanks for all your help. Les Quote Link to post Share on other sites
Mk2 Chopper Posted June 7, 2021 Report Share Posted June 7, 2021 Different earth's but same supply. I wonder if you could put the same question on the General TR forum, a guy called Bob, is good on electrics but I don't think comes on the '6 forum page. There might be a way to suppress the fluctuations, but he'd know more I think. Gareth Quote Link to post Share on other sites
Les Pettitt Posted June 7, 2021 Author Report Share Posted June 7, 2021 Thanks Gareth, Now posted on general technical forum which I have never used before. If I have to buy a new alternator that is fine but it would be a real downer if the lights still pulsed. Thanks Les Quote Link to post Share on other sites
Mk2 Chopper Posted June 7, 2021 Report Share Posted June 7, 2021 Exactly, hopefully you'll get some help on there to decide what to do next. Gareth Quote Link to post Share on other sites
RobH Posted June 7, 2021 Report Share Posted June 7, 2021 A battery has very low internal impedance (resistance) which means it is very difficult to change the voltage without a high current flow, which this isn't. Any joint in the connections to it add more impedance and makes it easier it is to change the voltage the further you get from the battery. it is possible that the alternator output is fluctuating but you won't usually see much directly across the battery. The fluctuations can be 'flattened out' by the resistance of the cables and connections between the two. That is why I asked about the connector block in the battery cable earlier, as that introduces a point where resistance may exist. Either way it still looks like an alternator fault, whether a bad joint exists or not. There is nothing on the car which can cause a fluctuation except something rotating. Since it stopped when the alternator was disconnected it is pretty likely that is the source. The only other thing is the fuel pump, but since that remained running when the fluctuation stopped, it is also pretty likely that is not the culprit. A final test you can do would be to put the bulb directly across the alternator supply as close to the alternator as you can get. Quote Link to post Share on other sites
SpitFireSIX Posted June 7, 2021 Report Share Posted June 7, 2021 9 hours ago, ntc said: Disconnect the three black wires that earth the speedo and see what happens Hi, Answer: No change to ignition warning lamp. Suggest you stay well away from all things electrical as you really have no clue & could cause damage to your wiring or heaven forbid yourself. Just except the truth and move on, as You are beginning to embarrass yourself. Sincerely, Iain. Quote Link to post Share on other sites
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