Ignition Warning Light problem - advice please!

[Bronteboxer]

Having got around to commissioning for the new season, I have just been running the engine and guess what - the ignition warning light is shining. It is shining brighlty when I rev the engine and going out at tickover on about 550 rpm. It is fluttering between off and bright when the engine is rev'd. In other words it suddenly seems to be working the wrong way round! The ammeter is showing a charge when rev'd and discharge when all the electrics are put on - headlights, sidelights, brake lights wipers etc.

I have tried gently cleaning the contacts in the control box, but no change with this. I do recall this happening once before some years ago and the problem just suddenly evaportated. But sadly not this time

Any ideas plase on how I can fix the problem please??

My delight at fixing the leaky carb and better cold starting evaporated in seconds once I saw the light - typical old car syndrome!!....

Thanks in anticipation of any help from learned folk in JCC land............

Graham Austin. Jupiter LDG 988.

[Forumadmin]

How to test a Lucas dynamo. Do a search on JowettTalk for dynamo and this comes up as Dynamo Test. Note the link to the Gallery article in the original. This is the methodical way; but I suspect the control box points need cleaning. Be careful not to knock the cut-out on as you may burn out the dynamo and get a nasty smell.

A quick test below or the full test in the Gallery https://jowettnet/forum/download/file.p ... &mode=view. Javelin has C39 PV dynamo. Jupiter has Lucas type C45 PV4.

To test a dynamo, you need a multi-meter which can read 30 volts DC (Direct Current). Any cheap meter will do this job, as you will normally either get the reading you want, or no reading at all.

Before testing the dynamo, check the two cables connected to the rear of the dynamo. Gently pull on the spade connectors to ensure that they are firmly soldered or crimped to the cable. Any loose connection here will play havoc with the charging circuit.

Repeat the check at the other end of these cables which is at the voltage control box.

WARNING: The following procedure involves working in the engine bay with the engine running. Ensure there is no loose clothing and keep your hands and the connections to the test meter clear of the fan blades. Have an assistant available to switch the engine on and off.

This procedure assumes positive earth. Reverse multimeter connections if you have changed to negative earth.


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Disconnect both cables from the connections at the back of the dynamo.

Set the meter to 30 volts DC.

Connect one lead from the meter to the chassis or body-work. Ensure a good electrical connection is made.

Connect the other lead of the test meter to BOTH terminals on the dynamo. You might need to twist a bit of wire around both terminals before connecting the lead from the test meter.

Start the engine and let it tick over. Connect the multi- meter's negative cable to the dynamo. Connect the meter's positive terminal to earth (somewhere on the car bodywork).

A reading of between 20 and 24 volts should be seen on the meter. This will vary depending on engine speed, but as a guide at about 750 rpm you should see about 15 volts, rising to over 24 volts at about 1,000 rpm. There is no need to rev the engine above 1,000 rpm when testing a dynamo. If the voltage reading is not present there is a fault.

* A reading of about 1 volt indicates a field winding fault.


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Confirm a field winding fault in the dynamo as follows;

Set the multi-meter to Ohms and measure the resistance between the field winding terminal F and the dynamo body. Make sure you get a good connection between the multi-meter probe and the dynamo body. The resistance reading should be 6.2 ohms. If the reading is different from this suspect that the insulated coils are touching the dynamo body OR that the field coils are disconnected.

There is really nothing you can do about that except replace the dynamo.

* If the reading is 4 or 5 volts the armature windings may be faulty.

* If the reading is zero then either a dynamo brush is completely broken or there is some break in the testing circuit. Repeat the test.

If there is definitely no voltage reading then the dynamo needs new brushes or must be replaced.

If the reading is within the ranges indicated (15 - 30 volts) but you still suspect a problem in the charging circuit, test the voltage at the control box end of the F and D cables. (Remember to replace the F and D cables to the dynamo). If the voltage is other than 15 - 30 volts then there is a problem in the wiring loom.

[Leo Bolter]

Hi Graham.

This may be "overkill" in answering your problem, but the address below takes you to a online book called MGB ELECTRICAL SYSTEMS. This could also be a great reference book for other automotive electrical knowledge/problem solving etc. I suggest making a browser shortcut to it for future reference.

http://books.google.co.nz/books?id=QwyK ... it&f=false

If you go to this site, then scroll down to pages 63 and 64, you may find your answer there (or at least some clues).

Simply put, I believe the charge warning light theory works like this:
When the ignition is turned on, (but the dynamo is not turning), a connection is established from a "live" 12 volt source to the warning bulb which eventually completes it's circuit to earth via a generator brush. The bulb light up.
When the generator is revolving and producing about 12 volts the voltage at the brush is "balanced" to the afore mentioned live connection (supplied by the ignition switch) so the bulb goes out.
Well that's the theory . . . sticky or worn brushes could be the culprit, amongst other things . . . I have a car with a alternator, and it's charge light glows so dimly when the car is being driven that it can only be seen glowing in the dark! I haven't been able to sort it, so have chosen to "fix it by applying ignore" . . . the battery doesn't go flat and they last at least 6 years, so the ignore method seems to be satisfactory!

[Forumadmin]

Link to diagram showing control box on Javelin. If you can read such a diagram it shows how current can flow through the ignition light in either direction based on the difference in voltage between the battery and the dynamo and any loads either side of the light. Firstly find out the voltage on either side of the lamp that will tell you which way the current is flowing i.e. the battery is giving out more than the dynamo. Then trace back to see where the volts are being lost either by a bad connection or a load or indeed incorrect wiring. This can happen if accessories are connected to the wrong place.

Simpler diagram to show current flowOne side of the warning light should be connected via the D terminal to the dynamo output. The other side should be connected via the ignition switch, A1 terminal , cut off coil, A terminal, through Ammeter to battery. Thus check volts at each of these points. If the cut off is closed then the dynamo is connected to the battery through the cut off coil and Ammeter. This happens when the dynamo volts is above the battery volts. The cut off closing also shorts out the warning light. There should not be cases of dim warning light or warning light on when engine is above 1000rpm. If there is, there is something wrong.

[Bronteboxer]

Thanks for all the compehensive advice chaps. Reading what has been said and in particular the comments from Leo explaining very simply the principal and adding this to the more detailed stuff from 'Forumadmin' I am going to check the power to the light as first step.

Logic says that if there is no light when the ignition is on with the engine not started and it goes from no light to dim to bright when the power is applied from the dynamo when started and revd, plus I can see a charge on the ammeter, then it could be the feed from the switch.

Another piece of the jigsaw which I didn't mention is that I recenty replaced the starter button and of course I had the dash out, so might have distured that supply. I did check everything before I pushed the lot back, but it could be the cause and its fairly a simple thing to check. I will also check the charge just to make sure thats in order.

Interesting that Leo sent me the MGB details. I have just put a mint original 10k only MGB on Carandclassic.co.uk (advert ref C218325) for sale!!

Hopefully I can get at this problem again tonight.

Many thanks again.

G.

[Forumadmin]

I thought I would try out the TOPIC Gallery for doing a tutorial on the control box. One reason I like the Gallery is it encourages you to use pictures to illustrate your words like a slideshow and it allows others to comment in context with the 'slide'.

Anyhow, try it out and add some comments. Note this link selects the album, so click on the first item in the album and click on next once you have read the page and added your comments.

P.S. We will be using this medium for 'Project B' as Gallery allows much better reformatting of our collected thoughts. There will be many 'tutorials' being given as we progress through the rebuild.

[Bronteboxer]

Firstly thank you chaps for your comprehensive replies.. This where the Forum really adds benefit to all of us running our Jowetts.

The problem is now solved, thanks to your excellent and valued help. In particular, thanks to Leo for his very straightforward explanation of the basic principals of the system. Which helped me determine a plan of action before getting into the workshop and commencing all checks.

Resolution:
When I restored the car about 18 years ago I fitted a new loom right through. The only piece of cable I didn't replace was the 6 inchs behind the dash from the Ignition light to the live feed. Guess what - it was this giving me the trouble hence the 'off when it should have been on and on when it should have been off' effect. As soon as this was rectified the problem disappeared. Sanity in the electrics department restored.

Now I just need to get my cold starting issues resolved and we will be away and running...........!!

In another post I have added a piece about 'bad/tired petrol'. This has been a problem this year for the first time - 2 differing marque cars. I now have this out of the way which confuses a lot of things in the 'poor running dept' and its onto the next set of tasks for a resolution.