johny Posted June 6, 2022 Report Share Posted June 6, 2022 1 hour ago, Chris A said: Got one! Somewhere in the bottom of my 'tools I never use' box. Solder? I think there might be a bit there as well. My first check will be to follow the route of the wire ( especially behind the dashboard in the mess there!) and loom to look for any obvious damage causing the short circuit. If the loom/wire is rubbing on something it could cause more trouble in the future so better to be safe than sorry. Second step, make a completely new length of wire from the bulb holder to pressure sensor as I'm convinced it is along this section that there is a problem. and keep us saddos on the forum fully informed of progress😁 Link to comment Share on other sites More sharing options...
Chris A Posted June 6, 2022 Author Report Share Posted June 6, 2022 2 hours ago, johny said: and keep us saddos on the forum fully informed of progress😁 Ok, as you asked. Checked the visible loom and wire under the bonnet all looks fine, although the wire from where it comes out of the loom and goes to the sensor is a bit (lot?) crusty and the insulation is broken in places but well away from anything. To be honest I was aware of this and it had crossed my mind (quickly) to do something about it. Under the dash, apart from it being messy, again no obvious fault. I did wonder if the bulb holder was shorting onto the back of the instrument unit, so pulled bulb holder out and let it hang free - still did the same. Put it back in and it appeared to be ok. Went for a run on the local bumpy lanes, fault did reappear. Still faint and intermittent, seems to get brighter/more frequent as the revs/speed rise - up to a point over 50mph it seems to stop. On the way back home I even wondered if the bulb itself could be the cause - swapped bulb still there. I am going to give the under dash area another check but I will order some new cable in the same colour combination (white + brown trace). As the postage is a bit more than the cost of wire I'm going to check my stock of connectors etc to see if there is anything else I need. I would prefer to be able to find the real cause in case it results in other problems. In the meantime I will use the car as it is clearly electrical not lubrication. And now for something completely different : I have to go and pick strawberries and raspberries in the garden, that's the afternoon taken care of. Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 6, 2022 Report Share Posted June 6, 2022 have you changed the bulb a failed filament sorting to the bulb case may be the culprit again its a cheap and easy swap in eliminating rather than illuminating Ha ! Pete Link to comment Share on other sites More sharing options...
johny Posted June 6, 2022 Report Share Posted June 6, 2022 cant see in this situation Pete as the bulb case holder isnt earth but connected to the wire that goes off to the pressure switch☹️ Link to comment Share on other sites More sharing options...
chrishawley Posted June 6, 2022 Report Share Posted June 6, 2022 2 hours ago, Chris A said: seems to get brighter/more frequent as the revs/speed rise - up to a point over 50mph it seems to stop ......is that with the wire connected to the oil pressure switch? Or disconnected from it? Link to comment Share on other sites More sharing options...
Chris A Posted June 6, 2022 Author Report Share Posted June 6, 2022 2 hours ago, Pete Lewis said: have you changed the bulb a failed filament sorting to the bulb case may be the culprit again its a cheap and easy swap in eliminating rather than illuminating Ha ! Pete Did wonder about the bulb being the cause : 3 hours ago, Chris A said: On the way back home I even wondered if the bulb itself could be the cause - swapped bulb still there. 2 hours ago, johny said: cant see in this situation Pete as the bulb case holder isnt earth but connected to the wire that goes off to the pressure switch☹️ Link to comment Share on other sites More sharing options...
Chris A Posted June 6, 2022 Author Report Share Posted June 6, 2022 2 hours ago, johny said: cant see in this situation Pete as the bulb case holder isnt earth but connected to the wire that goes off to the pressure switch☹️ I wasn't confident either but worth a try, after all no cost involved 🙄 Link to comment Share on other sites More sharing options...
Chris A Posted June 6, 2022 Author Report Share Posted June 6, 2022 1 hour ago, chrishawley said: ......is that with the wire connected to the oil pressure switch? Or disconnected from it? At that point it was still connected. I did think of stopping and disconnecting it but knowing my luck a neighbour would have driven past just as the bonnet was up, the reputation of British engineering would have been lost forever! As I have mentioned the fault is there even when the pressure switch is disconnected. It is erratic, after 'fiddling' under the dash it seemed to have been cured but within a couple of hundred metres it was back again. I'm going to have a VERY close inspection of the mess of wires under the dash next. As we all know to do that is "less than easy" and my back has to be having a good day or else I risk being stuck . .Picking strawberries & raspberries in the garden for over 2hours this pm did me in. It will NOT win, a draw is possible though 😠 Link to comment Share on other sites More sharing options...
cliff.b Posted June 8, 2022 Report Share Posted June 8, 2022 On 06/06/2022 at 17:00, Chris A said: At that point it was still connected. I did think of stopping and disconnecting it but knowing my luck a neighbour would have driven past just as the bonnet was up, the reputation of British engineering would have been lost forever! As I have mentioned the fault is there even when the pressure switch is disconnected. It is erratic, after 'fiddling' under the dash it seemed to have been cured but within a couple of hundred metres it was back again. I'm going to have a VERY close inspection of the mess of wires under the dash next. As we all know to do that is "less than easy" and my back has to be having a good day or else I risk being stuck . .Picking strawberries & raspberries in the garden for over 2hours this pm did me in. It will NOT win, a draw is possible though 😠 Just a thought, do you have any led bulbs? I am presuming that if you are getting a slight flicker then the current through any short is low, but it may still be enough to make an led come on brightly, thus aiding fault finding when wiggling stuff about. Obviously, polarity would have to be considered. Link to comment Share on other sites More sharing options...
Chris A Posted June 8, 2022 Author Report Share Posted June 8, 2022 6 hours ago, cliff.b said: Just a thought, do you have any led bulbs? Yes. All instrument and warning bulbs are LED except the red ign. light, and have been for quite some time. The LED for the oil pressure warning was changed a few weeks ago for a brighter one. When I swapped the bulb for another the other day it too was a LED but the less bright version. Maybe I should do a bulb swap and put in a filament version and see if there is a change. The short could have been there for ages but I never spotted it with the less powerful LED. You have to bear in mind the car is a convertible and is driven with the roof down all the time hence the reason for wanting bright warning lights to be visible in the sunny conditions Normandy is famous for.😎 I'll do a bulb swap tomorrow if I can get time free for the car. I have ordered some wire, correct colours, and a few other bits and pieces to make the postage worthwhile 6 hours ago, cliff.b said: Obviously, polarity would have to be considered Is it, my wife is bi-polar. One day with the penguins, the next with the polar bears. Link to comment Share on other sites More sharing options...
Colin Lindsay Posted June 8, 2022 Report Share Posted June 8, 2022 11 minutes ago, Chris A said: Is it, my wife is bi-polar. One day with the penguins, the next with the polar bears. I hate being bi-polar, it's brilliant! 1 Link to comment Share on other sites More sharing options...
cliff.b Posted June 8, 2022 Report Share Posted June 8, 2022 7 minutes ago, Chris A said: Yes. All instrument and warning bulbs are LED except the red ign. light, and have been for quite some time. The LED for the oil pressure warning was changed a few weeks ago for a brighter one. When I swapped the bulb for another the other day it too was a LED but the less bright version. Maybe I should do a bulb swap and put in a filament version and see if there is a change. The short could have been there for ages but I never spotted it with the less powerful LED. You have to bear in mind the car is a convertible and is driven with the roof down all the time hence the reason for wanting bright warning lights to be visible in the sunny conditions Normandy is famous for.😎 I'll do a bulb swap tomorrow if I can get time free for the car. I have ordered some wire, correct colours, and a few other bits and pieces to make the postage worthwhile Is it, my wife is bi-polar. One day with the penguins, the next with the polar bears. Aha, didn't realise the oil pressure light was already an LED. If barely flickering it could be due to an extremely small current or possibly even an induced voltage from something else. If this has happened since a newer/brighter LED has been fitted then I suspect there might not be a fault at all, just more sensitive or as you suggest, now visible. If you were to put a filament bulb back in then it may not do it at all. Link to comment Share on other sites More sharing options...
cliff.b Posted June 8, 2022 Report Share Posted June 8, 2022 Thinking further about the possibility of an induced voltage making an LED flicker, the oil pressure switch is pretty close to the distributor, how near does the wire pass near any HT leads? Might be worth disconnecting the wire and moving it well away from the engine and doing another road test (making sure the free end can't ground on anything as that might become confusing lol) Link to comment Share on other sites More sharing options...
NonMember Posted June 8, 2022 Report Share Posted June 8, 2022 24 minutes ago, cliff.b said: how near does the wire pass near any HT leads? It may not be the HT leads you need to worry about. The LED only needs a tiny voltage, so what matters is whether you can induce a few milliamps of current for a moment. Running parallel to the coil supply wire could do that, as long as there's enough capacitance to pump it into. I'm not really sure how much that would need to be. Link to comment Share on other sites More sharing options...
cliff.b Posted June 8, 2022 Report Share Posted June 8, 2022 17 minutes ago, NonMember said: It may not be the HT leads you need to worry about. The LED only needs a tiny voltage, so what matters is whether you can induce a few milliamps of current for a moment. Running parallel to the coil supply wire could do that, as long as there's enough capacitance to pump it into. I'm not really sure how much that would need to be. Exactly my thinking. There may not be a fault here at all. Link to comment Share on other sites More sharing options...
Chris A Posted June 8, 2022 Author Report Share Posted June 8, 2022 36 minutes ago, cliff.b said: Thinking further about the possibility of an induced voltage making an LED flicker, the oil pressure switch is pretty close to the distributor, how near does the wire pass near any HT leads? How close is 'pretty close'? The loom goes along the side valance to the bulkhead and does get quite close to the coil. As well as trying a good old filament bulb I think will also try a temporary wire going 'the long' way from the bulb to the sensor thus keeping well away from coil, distributor & HT leads. Isn't life just full of fun, at least I'm certain (🤞) there isn't a genuine oil pressure issue and can simply regard the problem as an exercise in practical electrics. 🙄 Thank to all the professors who are enlightening (💡) me. Ah, 18h30 - apéro time! Link to comment Share on other sites More sharing options...
johny Posted June 8, 2022 Report Share Posted June 8, 2022 1 hour ago, NonMember said: It may not be the HT leads you need to worry about. The LED only needs a tiny voltage, so what matters is whether you can induce a few milliamps of current for a moment. Running parallel to the coil supply wire could do that, as long as there's enough capacitance to pump it into. I'm not really sure how much that would need to be. But surely even with an induced voltage you still need a circuit - this problem occurs even if the wire from the light is disconnected at the pressure switch.... Link to comment Share on other sites More sharing options...
cliff.b Posted June 8, 2022 Report Share Posted June 8, 2022 40 minutes ago, johny said: But surely even with an induced voltage you still need a circuit - this problem occurs even if the wire from the light is disconnected at the pressure switch.... I was thinking that one side of the LED is connected to +12v and the engine end is just effectively a length of wire. If a voltage is induced in that wire which is different to 12v, there would be a voltage difference across the LED & a miniscule current may briefly flow through it, perhaps enough to make it flicker. It's only a theory and some further testing will hopefully show if it "holds water" or not. Link to comment Share on other sites More sharing options...
NonMember Posted June 9, 2022 Report Share Posted June 9, 2022 15 hours ago, johny said: But surely even with an induced voltage you still need a circuit Yes, which is why I queried the capacitance issue. If you induce voltage in a wire then it appears at the free end, not the bulb. Actually, you don't "induce" voltage, you induce current. You can get voltage from capacitive coupling, and the induced current can flow as long as there's somewhere for the charge to collect - i.e. a capacitance. Rather like you, I instinctively don't think this explanation holds water. However, stray capacitance and inductance are the bane of many a sensitive electronic circuit and LED bulbs are potentially quite sensitive. Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 9, 2022 Report Share Posted June 9, 2022 surely this is simple remove the LED fit the correct Bulb and see what you get that eliminates stray LED illumination back to the basics Pete 1 Link to comment Share on other sites More sharing options...
cliff.b Posted June 9, 2022 Report Share Posted June 9, 2022 5 minutes ago, Pete Lewis said: surely this is simple remove the LED fit the correct Bulb and see what you get that eliminates stray LED illumination back to the basics Pete I think this has got past the point of fixing it now and into the realms of trying to understand why it's doing it lol Link to comment Share on other sites More sharing options...
johny Posted June 9, 2022 Report Share Posted June 9, 2022 yes we want a definite fix as it may come back to bite again but trouble is if Chris runs a new wire we will never know if the problem was an earth fault or induced current😭 Link to comment Share on other sites More sharing options...
Pete Lewis Posted June 9, 2022 Report Share Posted June 9, 2022 I feel the Must Have has induced the current problem Ha ! dont have enough hair left to worry now Pete Link to comment Share on other sites More sharing options...
johny Posted June 9, 2022 Report Share Posted June 9, 2022 I dont have any hair either but cant sleep until we have an answer🥱 Link to comment Share on other sites More sharing options...
cliff.b Posted June 9, 2022 Report Share Posted June 9, 2022 20 minutes ago, johny said: yes we want a definite fix as it may come back to bite again but trouble is if Chris runs a new wire we will never know if the problem was an earth fault or induced current😭 I agree, but what can he do to prove one way or the other 🤔 Can only try various things and gather evidence, I guess. Maybe a test led connected to +12v and a trailing wire on the other terminal which he can waggle around the engine bay while looking closely for flickering 🙂 Actually, any of us could do that test ourselves lol Link to comment Share on other sites More sharing options...
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