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Ray White
Joined: 02 Dec 2014
Posts: 7140
Location: Derby
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 Posted: Thu Oct 16, 2025 5:54 pm Post subject: ignition warning light. |
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Please could someone help me diagnose what is wrong with this light. Before it stopped working altogether it needed a light tap to illuminate.
Now the light doesn't work when I switch on the ignition. I have checked the bulb and it is good.
I have a 12 volt reading from one terminal the (spring loaded central contact) but not the other.
If the bulb is OK, must the fault lie in the holder? or perhaps the bulb is not making contact with the sides of the holder? |
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MikeEdwards
Joined: 25 May 2011
Posts: 2713
Location: South Cheshire
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| Posted: Thu Oct 16, 2025 6:07 pm Post subject: |
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If the bulb is definitely OK, then surely it must either be the bulb holder, or the wiring to it.
_________________
1976 Vauxhall HP Firenza, 1976 Vauxhall Sportshatch (x2), 1986 Audi coupe quattro, 2000 Audi TT |
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Ray White
Joined: 02 Dec 2014
Posts: 7140
Location: Derby
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| Posted: Thu Oct 16, 2025 6:22 pm Post subject: |
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| MikeEdwards wrote: | | If the bulb is definitely OK, then surely it must either be the bulb holder, or the wiring to it. |
How could I test the holder without taking it out of the dashboard? If I use the buzzer on my multi meter, should I expect continuity between the sides of the holder and earth?
It is also possible that there is a poor contact between the bulb and the sides of the holder. Perhaps this is the problem? |
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ukdave2002
Joined: 23 Nov 2007
Posts: 4242
Location: South Cheshire
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| Posted: Thu Oct 16, 2025 6:35 pm Post subject: Re: ignition warning light. |
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| Ray White wrote: | | Please could someone help me diagnose what is wrong with this light. Before it stopped working altogether it needed a light tap to illuminate.? |
well it has to be a poor connection, if the bulb is good that only leaves the holder, pop it out and try it on the bench. Is anything pressing on the holder, it may be flexing resulting in less than perfect contact with the bulb? |
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alastairq
Joined: 14 Oct 2016
Posts: 2121
Location: East Yorkshire
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| Posted: Thu Oct 16, 2025 7:24 pm Post subject: |
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I'd try another bulb....just in case it's a dodgy filament?
_________________
Dellow Mk2, 1951 built, reg 1952.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
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Ford Pop chassis, Ashley 1172 bodyshell, in pieces. |
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Ray White
Joined: 02 Dec 2014
Posts: 7140
Location: Derby
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| Posted: Thu Oct 16, 2025 9:35 pm Post subject: |
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| alastairq wrote: | | I'd try another bulb....just in case it's a dodgy filament? |
The bulb is 100%. The problem is probably of my own making. I couldn't use the bulb that came with the fitment as it was too high a wattage for the plastic lens when the resistor wire became broken and of no use.
The only bulb I could find was incorrect for the holder which is why I suspect a poor contact may be the problem. I thought I had made a good job of it but perhaps it was more a case of wishful thinking on my part. |
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Ray White
Joined: 02 Dec 2014
Posts: 7140
Location: Derby
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| Posted: Thu Oct 16, 2025 9:44 pm Post subject: Re: ignition warning light. |
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| ukdave2002 wrote: | | well it has to be a poor connection, if the bulb is good that only leaves the holder, pop it out and try it on the bench. Is anything pressing on the holder, it may be flexing resulting in less than perfect contact with the bulb? |
Unfortunately, the holder is trapped by the dash covering and any attempt to remove it will spoil the leather. I have been trying to think how I could test the holder (the sides are what make contact with the bulb) with it left in situ.
I am thinking if the holder sides have continuity with the wire then the problem is that they must be too slack to hold the bulb. I suppose without the bulb making a good contact I will not get a reading from the wire anyway.?
I find these ignition warning lights are a strange anomaly with one source of power set against another. |
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ukdave2002
Joined: 23 Nov 2007
Posts: 4242
Location: South Cheshire
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| Posted: Fri Oct 17, 2025 6:45 am Post subject: |
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| Ray White wrote: | The bulb is 100%. The problem is probably of my own making. I couldn't use the bulb that came with the fitment as it was too high a wattage for the plastic lens when the resistor wire became broken and of no use.
The only bulb I could find was incorrect for the holder which is why I suspect a poor contact may be the problem. I thought I had made a good job of it but perhaps it was more a case of wishful thinking on my part. |
Why not simply add a resistor to the bulb circuit, so that the correct bulb can be used for the fitment? |
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MikeEdwards
Joined: 25 May 2011
Posts: 2713
Location: South Cheshire
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| Posted: Fri Oct 17, 2025 8:43 am Post subject: |
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The problem with trying to test continuity in the bulb holder is that it might be variable - you might happen to put your meter probes in a spot where there is good contact, but you'd need to make sure that is where the bulb is going to touch as well.
I spent ages trying to get consistent results in my tail lamp bulb holders when I was putting the Sportshatch back together, they're really easy to access and remove but it was still a pain, so I understand your frustration.
_________________
1976 Vauxhall HP Firenza, 1976 Vauxhall Sportshatch (x2), 1986 Audi coupe quattro, 2000 Audi TT |
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Ray White
Joined: 02 Dec 2014
Posts: 7140
Location: Derby
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| Posted: Fri Oct 17, 2025 8:55 am Post subject: |
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| ukdave2002 wrote: | | Ray White wrote: | The bulb is 100%. The problem is probably of my own making. I couldn't use the bulb that came with the fitment as it was too high a wattage for the plastic lens when the resistor wire became broken and of no use.
The only bulb I could find was incorrect for the holder which is why I suspect a poor contact may be the problem. I thought I had made a good job of it but perhaps it was more a case of wishful thinking on my part. |
Why not simply add a resistor to the bulb circuit, so that the correct bulb can be used for the fitment? |
Of course you are right. This is what I should have done when I had the chance but I made the wrong choice. It all seemed to work O.K. at the time but it is rather too late now as I can't get to anything without messing it all up.
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V8 Nutter
Joined: 27 Aug 2012
Posts: 602
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| Posted: Fri Oct 17, 2025 9:31 am Post subject: |
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| Had a similar problem with the brake light on a Dodge, but that was only 6 volt. Put a new bulb in it worked sometimes, put the old bulb back in it worked every time. The diameter of the new bulb was very slightly smaller, so it didn't make a good contact to earth. |
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Penman
Joined: 23 Nov 2007
Posts: 4866
Location: Swindon, Wilts.
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| Posted: Fri Oct 17, 2025 10:41 am Post subject: |
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Is there a conductive paint/lacquer that could increase the diameter of the bulb slightly so that it fits better?
_________________
Bristols should always come in pairs.
Any 2 from:-
Straight 6
V8 V10 |
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ukdave2002
Joined: 23 Nov 2007
Posts: 4242
Location: South Cheshire
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| Posted: Fri Oct 17, 2025 10:49 am Post subject: |
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| Solder wires directly to the bulb, drill the back of the fitment out and connect directly to the loom, a bit brutal but sometimes needs must and saves messing with the dash covering. |
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ukdave2002
Joined: 23 Nov 2007
Posts: 4242
Location: South Cheshire
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| Posted: Fri Oct 17, 2025 12:13 pm Post subject: |
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| Solder wires directly to the bulb, drill the back of the fitment out and connect directly to the loom, a bit brutal but sometimes needs must and saves messing with the dash covering. |
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Ray White
Joined: 02 Dec 2014
Posts: 7140
Location: Derby
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| Posted: Fri Oct 17, 2025 4:17 pm Post subject: |
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I am getting continuity from both external terminals of the bulb holder with readings taken from relevant points inside the holder. As the bulb is OK I am thinking it must be a problem with a wire further away.
I did make sure of a snug fit for the bulb by lining the inside of the holder with brass shim. It is making a good contact but not illuminating so I guess the problem is not the holder /bulb as I first thought.
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THAT was it. Nothing more than a separated bullet connector. I think more clearly when I am not too tired.
All I need to do now is find out why my headlamps are not working properly.  |
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