Ignition warning light

[Woodyalan]

Can anyone suggest what this fault is? After a long lay up I started the Traveller and found the ignition warning light staying on. On other cars the fault has been either control box or dynamo. As control boxes are cheap I got a new one but it made no difference. I noticed the cut out points never closed on the old box or the new one whatever the engine was doing. Next I tried a new dynamo and polarised it but still no change. When I switch ignition the red light comes on and now goes out while the revs are low. When I then raise the revs the light comes back on and burns brighter as revs are increased eventually causing the bulb to blow. I put a new bulb in which also blew within seconds of switching ignition on. Thanks for any help.
Alan

[myoldjalopy]

Well, this is a bit odd, as your original problem of the ign. lamp not going out suggests the charging system wasn't working - fan belt too slack, a faulty dynamo, faulty control box or a wiring fault.
But now that the bulb is blowing it suggests over-charging. Have you cleaned the contacts in the new control box?
"I put a new bulb in which also blew within seconds of switching ignition on." Are you saying the bulb blew without even running the engine? If so, that's even more odd. Can you get a reading off the battery when revving the engine?

[Woodyalan]

Hi MOJ
I rubbed sandpaper through the contacts before fitting the control box. The second bulb did indeed blow with just ignition switched on. I have connected a wire between the two dynamo terminals and a voltmeter between that and battery earth. The readings are not consistent and tend to disappear when engine is revved but I have seen readings between 16 and 19. Observing the cut out points I have seen no movement at all, they are always in the same open position.

[myoldjalopy]

I wouldn't have used sandpaper on a new control box. Just wipe them over with thinners. Manuals are quite specific that the cut-out contacts should be rubbed with fine glass paper and the regulator contacts with emery or carborundum paper, but I don't see that as being necessary with a new box.
I would expect readings from the dynamo to gradually increase as you raise the engine, not be inconsistent and disappear as you increase the revs. Of course, over-revving can damage the dynamo if the regulator is not connected or working. What reading do you get at the battery when all is connected up as it should be? It should be 'around' 14v with the engine running briskly.
Now, this next is purely guesswork, but it is possible the old control box wasn't working because of oxidation on the cut-out points, due to the 'long lay-up' and thus the red light never went out. Rubbing both sets of points over-enthusiastically on the new box with sandpaper may have damaged these and so they then didn't cut out, as you say. Then, with a new dynamo it may be that the control box regulator also wasn't doing its job, voltage rose and blew the bulb - and damaged the new dynamo, which is now showing wierd and fluctuating readings. But I can't think why the bulb should blow if the engine wasn't running.......anyone else?

[Woodyalan]

MOJ
With everything connected and engine running at brisk idle I am getting just under 12 volts at the battery. Revving the engine makes no difference to the reading. I presume that as the cut out points remain open no charging can take place anyway, the old control box was the same. I tried connecting the dynamo terminals together again to check with voltmeter and was getting a reading of about 10 at a brisk idle. When I try increasing revs for some reason the reading seems to disappear except for momentary flashes which can be around 16 to 19. As I said before the ignition light was coming coming on and burning brighter as revs increased apparently causing the bulb to blow. What could be causing that?
Alan

[myoldjalopy]

Yes, if the cut-out doesn't operate, the battery will not charge, which is suggested by your poor reading at the battery when trying to charge it.
Your tests on the dynamo suggest that it is not working properly either - its output seems very erratic from your test results. I had one like this once, readings were all over the place. My best guess at a distance is both the dynamo and the control box are not working properly so that when the dynamo does give flashes of a higher charge (you mention readings of 16 - 19v), it is not regulated and the ignition bulb blows. The control boxes available now aren't of great quality compared to the 'proper job' good old ones and have been known to give early failure. I did have a situation once where a faulty control box goosed the dynamo and I had to replace both
I would double-check electrical connections are secure and if still no good, replace both the control box and dynamo (again, I know, but neither appear to be working properly from what you say). Or find someone who is well-versed in vintage car electrical systems to investigate and do further tests but that might prove to be even more expensive, especially if they confirm my theory!
The other option would be to do away with both control box and dynamo, go -ive earth and fit an alternator............but if the dynamo and control box components are good it will work, assuming all wiring is correct and secure.

[geoberni]

My understanding of the niceties of the voltage control of the dynamo are somewhat rusty, as I haven't practised it since my basic technical training as an electrical engineer in the mid 70s.
But there are 2 things I can be 100% certain of without taxing my 'little grey cells' excessively.....

I rubbed sandpaper through the contacts before fitting the control box.

That's probably the worst thing you can do. The surfaces need to be smooth and ideally 'polished' in appearance. All sandpaper does is rough the surfaces up and effectively age the contact surfaces many years, potentially causing them to stick together.

The second bulb did indeed blow with just ignition switched on.

Well I'm afraid you must have simply put the wrong rating bulb in then; because the only voltage source available to the lamp, until the Dynamo is turning over at a reasonable speed, is the Battery.
If you had a 12 volt lamp fitted it couldn't have blown as soon as the ignition switch was on. Simple law of physics.

[myoldjalopy]

Which supports my idea that rubbing the control box points with sandpaper damaged it, consequently this then caused damage to the dynamo, so the whole system is kaput.
And geobernie's theory about the wrong rating bulb does sound highly probable as I can't think of an alternative reason for the bulb to blow with ignition on only!

[oliver90owner]

As I recall, there were different connections required for the control box for positive and negative earth operation.

It is a long time since I have had anything to do with charging control boxes but I would not be surprised if modern items only work with one polarity? Dynamo systems were discarded, to be replaced with alternators, on my Cortinas and Anglias from the late ‘60s/early ‘70s. Dynamos just would not run auxiliary lighting and halogen headlamps (up to 100W versions) .

[Woodyalan]

Thanks chaps
It's already neg earth btw. I may well go the alternator route but it would have to be the full conversion kit and none of the usual suppliers have them in stock at the moment.
Alan

[geoberni]

As I recall, there were different connections required for the control box for positive and negative earth operation.

No, the only thing to do with the generating system is to 'flash' the dynamo Filed windings to change the polarity of the residual magnetism in the windings.
Other than changing the battery connections over, the only other wiring change is the Coil connections, to ensure the spark is the right direction, i.e. from Plug centre electrode to the body and not the other way around. It'll still run without changing the connections, but the spark is up to 50% weaker.

Incidentally, I've just found a good run through of how the Dynamo charging system works here: http://www.mgb-stuff.org.uk/controlbox.htm

[geoberni]

Alan,
Regarding the lamp blowing, could you have inadvertently fitted an MM/early SII Ignition Warning bulb, because they are only 2.5v for some reason.

There's nothing to readily indicate why on the wiring diagram; it must be something to do with the build layout of the Controller. There is an extra winding in the early Controllers, with the built in fuse holders.

[Woodyalan]

Geoberni
The bulb was the screw in type identical to the first blown one but not new so could have been dodgy. What you were saying before about changing connections on the coil, the manual shows a white wire going to switch terminal and a white with black coming from the contact breaker terminal but this is when earth is positive. Does this mean they should be the other way round with a negative earth? Mine is negative earth but wired as in the manual with white/black going to the contact breaker. As you say it will work either way round.
Alan

[myoldjalopy]

Yes, the manual shows the correct wiring for +ive earth. If your car is now -ive earth just loosen the coil in its bracket and twist it through 180 degrees so the connections are the other way round. You may have to take out the king lead to do this or it could twist in the process. As 'geobernie' says, this will give you a stronger spark.

[geoberni]

HI Alan
yes, perhaps the lamp wasn't up to spec for whatever reason.
As to the coil connections, I raised a topic on it early last year: viewtopic.php?f=12&t=70183

[Woodyalan]

Sorry but I'm going cross eyed reading the instructions. For neg earth should it be white/black to SW then white to CB. Many thanks!
Alan

[myoldjalopy]

Yes! Just swivel the coil round like I described above. Basically the coil has to be connected the opposite way to what you have now.....

[Woodyalan]

MOJ or Geoberni
I'm probably being really thick here but why do you need to physically turn the coil round, is it not just a case of reversing the connections on the coil?
Alan

[myoldjalopy]

Yes, if you can simply do that. I'm just thinking that swapping the wires across may not be possible, depending on how long they are - and it may look a bit odd with the wires crossing over. It will look neater if you simply twist the coil in its bracket 180 degrees, after loosening the clamp, of course. But you can decide after looking at the set-up in your car which way you want to go.
Thinking further, it may not be such an issue if your coil is mounted on the dynamo/alternator, but mine is mounted on the bulkhead and the way I suggested is what I would do in my case.

[geoberni]

Yes, just swap the 2 white-ish wires over, I say white-ish as it depends on how old your wiring is.

I found the pencil trick I posted about was most useful to ensure I had got it right. Basil's Coil used to be on the Dynamo, but I moved it back to the bulkhead where it had originally been after I had a Coil failure.