Les Pettitt Posted June 3, 2021 Report Share Posted June 3, 2021 Hi All, Started the car the other day and noticed the interior light was flickering (pulsing) at maybe 2 to 3 times per second. Same rate of flicker (pulsing) when increased revs to 2,000. Main/dip beam also flicker. The only job I have done lately is replace the fuel tank so totally baffled. I have put on a brand new battery but made no difference. The volt gauge shows around 15 volts so the alternator appears to be working ok. Any ideas? Thanks Les Quote Link to post Share on other sites
RobH Posted June 3, 2021 Report Share Posted June 3, 2021 (edited) May be a bad connection in the lighting circuit which is making/breaking under vibration? I take it this doesn't happen with the engine off? First thing I would check is the fuse which drives the lighting circuit. It might be loose in the holder. If that is OK look at the voltage on that fuse and see if it is fluctuating - either with a meter or a bulb fitted with wires. If the fluctuations are there, the problem is between the fuse and the alternator/battery connection. If there is no fluctuation look at the wiring between the fuse and the lighting switch. (That switch is probably OK because it doesn't power the interior light). Edited June 3, 2021 by RobH Quote Link to post Share on other sites
Les Pettitt Posted June 3, 2021 Author Report Share Posted June 3, 2021 Thanks Rob, No problems with engine off. I'll get the meter out on the fuse box. Grateful for your help. The older I get the less I seem to think logically about these problems. Regards Les Quote Link to post Share on other sites
RobH Posted June 3, 2021 Report Share Posted June 3, 2021 If you do try to use a meter to check this Les, beware that a digital one probably won't show it if the fluctuation is fast. You really need an old fashioned analogue meter for that - or the bulb-on-wires as I said. Quote Link to post Share on other sites
Les Pettitt Posted June 3, 2021 Author Report Share Posted June 3, 2021 Good point Rob, I have both types of meter so will use the analogue. If that doesn't show anything I have a bulb on wires already made up that I keep in the glove box as an emergency inspection light. I do hope it is just dirty contacts in the fuse box. Thanks Les Quote Link to post Share on other sites
Les Pettitt Posted June 4, 2021 Author Report Share Posted June 4, 2021 Hi All, I cleaned the fuses and terminals with wire wool, started the car and used my analogue meter on each end of each fuse and the results were consistent in that the needle moved a max of one half of its width, ie less than half a volt max variation. But I can still see the lights pulsing similar to using the indicators at tickover. My tickover is not the smoothest so I don't know whether that would have an effect. One good thing to come out of my investigation is that I found the terminal in the fuse box that goes to the inertia cut off switch feels as though it is about to snap off. It is very loose and I can wiggle it without any movement to the fuse carrier so I shall replace the fuse box. Any other ideas? Am I just being paranoid? Regards Les Quote Link to post Share on other sites
John L Posted June 4, 2021 Report Share Posted June 4, 2021 Control box in the alternator, one the diodes faulty, giving not a smooth alternating current output, perhaps. Which alternator is fitted? John Quote Link to post Share on other sites
RobH Posted June 4, 2021 Report Share Posted June 4, 2021 Certainly sounds as though it is on the generator side of things - Is the fan-belt slipping perhaps? Does your car have the battery cable with the power take-off joint in it? If so it's worth checking that connection too. Quote Link to post Share on other sites
Les Pettitt Posted June 4, 2021 Author Report Share Posted June 4, 2021 Hi John, Alternator is labelled CJF Rotating Technologies Rep Lucas A103 08004004 Batch R52672 I bought it in 2004 from A&P Electronics, Hereford as I was looking for a 45 amp or 55 amp alternator at the time. Rob, The fan belt is definitely not slipping and yes, my battery cable does have a power take off joint. I have never messed with that cable, does the joint just pull apart? I agree it sounds as though it may be time for a new alternator. At least we could then eliminate that as a problem. What is the latest thinking on the best alternator and preferred supplier? Regards Les Quote Link to post Share on other sites
RobH Posted June 4, 2021 Report Share Posted June 4, 2021 The thinner wire just plugs in - the main part on the thick cable doesn't come apart. There are plenty of sources for equivalent alternators (but just swapping it out seems an expensive way to do fault-finding!) An 18ACR is usually offered as a replacement but an A127 has more output, e.g. - . https://www.autoelectricsupplies.co.uk/product_list/168 https://www.autoelectricalspares.co.uk/111185-alternator-43a-18acr-replaces-lucas-lra103-2380-p.asp Quote Link to post Share on other sites
John L Posted June 4, 2021 Report Share Posted June 4, 2021 Why not ask A&P electronics if they can offer a cause for your flickering, and perhaps a repair. John Quote Link to post Share on other sites
Mk2 Chopper Posted June 5, 2021 Report Share Posted June 5, 2021 Loosen the fan belt and remove it from the alternator and see if the flickering is still present when the engine is running. Quote Link to post Share on other sites
SpitFireSIX Posted June 5, 2021 Report Share Posted June 5, 2021 Sounds like regulator is toast Quote Link to post Share on other sites
Michael Mckiernan Posted June 5, 2021 Report Share Posted June 5, 2021 5 hours ago, Mk2 Chopper said: Loosen the fan belt and remove it from the alternator and see if the flickering is still present when the engine is running. Good place to start , do not pull the plug out of the alternator and run the engine easy way to fry a alternator. Mick Quote Link to post Share on other sites
astontr6 Posted June 5, 2021 Report Share Posted June 5, 2021 22 hours ago, Les Pettitt said: Hi All, I cleaned the fuses and terminals with wire wool, started the car and used my analogue meter on each end of each fuse and the results were consistent in that the needle moved a max of one half of its width, ie less than half a volt max variation. But I can still see the lights pulsing similar to using the indicators at tickover. My tickover is not the smoothest so I don't know whether that would have an effect. One good thing to come out of my investigation is that I found the terminal in the fuse box that goes to the inertia cut off switch feels as though it is about to snap off. It is very loose and I can wiggle it without any movement to the fuse carrier so I shall replace the fuse box. Any other ideas? Am I just being paranoid? Regards Les Hi Les, What size alternator have you got if its a 15ACR with a Bosch Pump this in my view is a boarder line power supply. I had this type of problem years ago and went over to an 18ACR and never had a problem since, plus the indicators worked properly on tick over waiting to turn right or left. Bruce. Quote Link to post Share on other sites
Mike C Posted June 5, 2021 Report Share Posted June 5, 2021 " noticed the interior light was flickering (pulsing) at maybe 2 to 3 times per second. Same rate of flicker (pulsing) when increased revs to 2,000"- so the flickering rate stays the same regardless of engine speed? If you have a good battery and it's doing this I don't think it's your alternator. Quote Link to post Share on other sites
ntc Posted June 5, 2021 Report Share Posted June 5, 2021 I have said this before make sure you have a good earth on the interior lights Quote Link to post Share on other sites
RobH Posted June 5, 2021 Report Share Posted June 5, 2021 OK so sticking to the facts we know: Both the interior light and main/dip beams flicker at 2-3 Hz. (so maybe something in the common feed to those circuits) There is a measurable 0.5 volt pulsation at the fuse box (that probably eliminates any effects from bad earthing since it effects more than one circuit, and points to it probably being up-stream of the fuse box) It only happens with the engine running (so must be associated with vibration, something rotating or something that only takes current with the ignition on) It is apparently not speed related and the voltmeter indicates 15V (that is problematic as it points to it not being the alternator or its regulator, though a (very) short run with the fan-belt off will be definitive on that) If the pulsing is still there during that test I would look at the power take off to the petrol pump. That takes a lot of current and if there is a bad joint it could possibly be that causing a cyclic voltage drop which affects everything else. Remember, the only work recently undertaken was on the petrol tank...... Quote Link to post Share on other sites
Les Pettitt Posted June 5, 2021 Author Report Share Posted June 5, 2021 Thanks All, Looks like a bit more investigation is needed before I scrap the alternator. I think the idea to loosen the alternator is excellent. I'll give it a try and report back. I'll also take a look at the wiring to the Bosch pump. I used to have a 50amp cable to the pump via a relay but when I got my car back from a very stressful and hugely disappointing three year restoration I found that the restorer had used my horn relay for my J type overdrive and my pump relay for the horns. So feed to the pump is now just via the (new) loom. I will post a new topic about relays and the J type when I have solved the flickering problem. I agree it does seem odd that the frequency of the flickering doesn't appear to alter with revs. I guess this may point towards the fuel pump wiring which I suppose has a pretty constant load irrespective of revs. The car starts better than it has ever done and the main beams flicker as well as the interior lights. Thank you all so much for your suggestions. Regards Les Quote Link to post Share on other sites
Les Pettitt Posted June 5, 2021 Author Report Share Posted June 5, 2021 Hi All, I couldn't wait, so I had to try mk2 chopper's suggestion and removed the fan belt. No flicker at all. I couldn't believe it so I reconnected the fan belt and alternator and again had flicker. Then removed the fan belt again and no flicker. So it looks like it must be the alternator at fault. I'll send a message to the supplier of the alternator (A&P electronics, Hereford) and see if they think it is worth a repair. Bit of a pain as I no longer work in Hereford, otherwise it would be easy to pop in. Maybe a new 18ACR is the way to go. Thanks for all your help, I would never have thought of taking the alternator out the circuit Regards Les Quote Link to post Share on other sites
ntc Posted June 5, 2021 Report Share Posted June 5, 2021 If you have a bad contact with the ignition light bulb or it’s earth the same thing will happen Quote Link to post Share on other sites
Mk2 Chopper Posted June 5, 2021 Report Share Posted June 5, 2021 At least you have a direction to go in now. Gareth Quote Link to post Share on other sites
SpitFireSIX Posted June 6, 2021 Report Share Posted June 6, 2021 20 hours ago, ntc said: If you have a bad contact with the ignition light bulb or it’s earth the same thing will happen Ignition light has no earth. Bad contact or removal of ignition light bulb will make no difference. Sorry, both wrong guesses. Quote Link to post Share on other sites
ntc Posted June 6, 2021 Report Share Posted June 6, 2021 36 minutes ago, SpitFireSIX said: Ignition light has no earth. Bad contact or removal of ignition light bulb will make no difference. Sorry, both wrong guesses. I don’t guess and you have invented a new electricity system Quote Link to post Share on other sites
SpitFireSIX Posted June 6, 2021 Report Share Posted June 6, 2021 (edited) 20 minutes ago, ntc said: I don’t guess and you have invented a new electricity system No, you Sir have invented it. Edited June 6, 2021 by SpitFireSIX Quote Link to post Share on other sites
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