Ignition Lamp

[yellowbelly]

I'm running a Marina 1.8TC based LWB Roadster. According to knowledgable senior members of the club who have seen it and know its history, it is unusual in that it appears to have everything from the donor vehicle, including the loom and the instruments.

On a day out yesterday, I noticed that the ignition warning lamp had stopped coming on as expected when the ignition is on, but the motor isn't running.

I have checked the obvious - the charging system is operating correctly; the bulb is OK; the in line fuse is OK. The wiring at the alternator and the ignition switch looks fine.

Any ideas? The dash is boxed in, so before I spend a weekend chasing the wrong thing, I'd appreciate comments.

As far as I am aware, running it without the lamp will not cause further problems, so I could just live with it, or fit a voltmeter I suppose, but it would be nice to retain it.

[greyV8pete]

If you have an alternator fitted that bulb is needed so the small current drawn tells the alternator to start charging.

[yellowbelly]

Thanks - it is indeed a dynamo; the donor was a 1971 model, and the alternator came with the mk2 in 1974, according to haynes.

[yellowbelly]

After checking everything again, I found that the charging system was no longer working, so I took the alternator to the excellent Mark's Electrical Services in Burslem, Stoke on Trent.

He very quickly diagnosed a 'lazy' regulator, and said that he will order and fit a replacement for about £25.

[redmonty]

After checking everything again, I found that the charging system was no longer working, so I took the alternator to the excellent Mark's Electrical Services in Burslem, Stoke on Trent.

He very quickly diagnosed a 'lazy' regulator, and said that he will order and fit a replacement for about £25.

That is really interesting to hear about the symptoms and diagnosis. Mine is also a Marina 1.8TC based kit. The guy who originally built it worked at Westlands helicopters and someone there made a new wiring loom for it using helicopter grade wiring in 1985. It has been off the road for 20 years and I can remember the red ignition light always used to work... but not anymore! I have checked the bulb and it works. At the moment I have just got to the stage of starting her up and am satisfied that the engine is OK. But I have been wondering what is up with the ignition light? Looks like I will need to investigate properly.

Mine was based on a 73/74 TC estate I think! I assumed it had an alternator? Looks like one but I'm no expert.

[redmonty]

Just checked... defo has an alternator.

[yellowbelly]

After fitting the repaired alternator, I still have no ignition lamp, and no charge. There are two leads to the alternator - a thick one which is the power supply, and a thinner one which signals the unit to start charging.

There is 12v at the power supply, but nothing at the signal lead. This appears to go via the ignition switch and the ignition lamp, so I am currently trying to establish where this is non-continuous.

On the day that the problem appeared, I had gone over a large pothole, and suspect that a contact has fallen off, but finding it is proving tricky, because of the poor access.

I'll keep you posted, as they say.

[greyV8pete]

Have you checked the ignition warning lamp bulb. If you have fitted a new bulb have you checked that too! Is the earth strap from the engine to the chassis ok? Is the ignition switch faulty?

[yellowbelly]

Thanks for that . Bulb and holder re-tested, and engine earth OK. I think that either the ignition switch has a fault, or more likely a break somewhere in the circuit. I'll check further in the next few days.

[yellowbelly]

I simply cannot identify a break in the circuit, so I am considering bypassing the old ignition warning lamp. I assume that a switched feed to a new bulb/holder, then on to the alternator would fix the problem.

Any thoughts?

[Ye Ol Ripper]

Have you done a continuity test on the back of the ignition switch to see if that is the problem? You might also discover a spade terminal has fallen off after you hit the bump in the road. If the car dash has an ampmeter fitted, ensure both connections at the back of it are on, as otherwise you won't get a feed to the ignition switch. A simple test to rule out the amp meter possible issue is do any other electrical items work on the car such as sidelights?

Also assuming you have glass fuses, have you spun them in their holders to ser if the ignition lamp then works.
You can also do a continuity test across each fuse, to ensure they are not blown.

[yellowbelly]

Thanks for that - it is just the sort of thing that I have been doing, so it is good to hear that I'm on the right lines.

The wiring appears to be the Marina loom, lengthened here and there but otherwise standard. The instruments too are straight from the donor - two dials and the various warning lamps in a single plastic housing. According to Haynes, there is a switched positive supply which is common to all of the instruments etc; it may be a fixed copper strip or similar within the unit. As the tacho, fuel gauge etc are all working, I'm starting to think that the break must be in that unit, which is going to be difficult to remove, and to diagnose. Accordingly, bypassing it may be a possibility, with a new ignition lamp mounted separately, at least until the Winter when I should have time to deal with it.

I'm still considering my options.

[Ye Ol Ripper]

I also have an adaption of the Marina wiring. Have you checked the white plastic connection that has approx 4 round pins in it( male & female plugs)?
On my car, it is situated
between the clutch master cylinder & the distributor. If the connection has separated or has corroded pins within, then you won't get an ignition feed into the car.

[yellowbelly]

I tried to bypass the old ignition lamp. It worked in that the new lamp came on when the key was in the ign position, then went out when the engine was running, with the battery charging OK.

But when I switched off, the engine continued running until I disconnected my new circuit. It has also caused further problems in that the indicators and tacho no longer work - I hope it's just a fuse somewhere that I haven't yet found.

I think that I'll leave it for a while.

[yellowbelly]

For anyone who is still interested, a mate came over and ran through it all with me.

It appears that the initial fault was caused by the small contact in the instrument binnacle, which supplies the ign warning bulb. It was getting power, but was not making contact with the bulb, so there was no circuit.

My thinking re bypass circuit was sound, but I had used a 25w bulb in the test wiring, simply because that was what I had to hand. When we replaced this with the bulb from the warning lamp. it all worked perfectly. Why this is I've no idea, but If I'd waited for the new bulb & holder that is on order, it would be sorted by now.

The other issues were probably caused by my taking a fuse out, testing it, then replacing it in a different alignment.

The new warning light will be in the dash below the binnacle, and while it is dismantled, I may fit a clock. Apart from that, I'm hoping that there will be no other issues with the wiring.

Maybe this saga will be of help to someone....