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Ignition Light On While Driving

SDJHAWK

Freshman Member
Offline
Hello Everyone,

New member hear with what I hope will be an easy question to answer, with an even easier solution.

My ignition light stays on while I am driving and never goes off. I was under the impression that this light turned off when the battery was recharged. I tested the generator and it is running like a top and output is good. The current battery is new as of May and should not need an extraordinary amount of recharging. My questions are: 1. Am I correct in thinking that the light should turn off after a full charge is attained, and 2. If I am correct what could be going on with the light, i.e. where should I start looking for this bit of trouble?

Thanks for all of your help, I need to get this resolved, the wife keeps asking for a "date night!"
 

Dave Russell

Yoda - R.I.P
Gold
Offline
The light is connected between the battery & the generator output. Before the engine starts, current is flowing from the battery (about 12.6 volts) through the light to the generator (zero volts). When the generator starts putting out, it's voltage rises to about 14 volts, the battery voltage also rises a bit, & with now nearly the same voltage on both sides of the light, it goes out.

In very rare cases, if a generator were putting out considerably more than 12.6 volts, There would be maybe 18 volts on one side of the light & 12.6 volts on the battery side & the light would again come on due to too high generator output.

First, check voltage at the large generator terminal to ground with a good meter & see if it rises to about 14 volts as the engine is speeded up. The voltage at the battery terminal should rise in a similar manner. If not, there are generator, regulator, wire connection problems, or a very loose belt.

There are several detailed references on the internet for checking the charging system. Here is one that may help. I'm not sure where it came from:
-------------------------
How to test a Lucas dynamo

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. This may be under the glove box on many small Fords, or mounted on the near-side inner wing, in the engine bay.

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.

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.

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.
------------------------------
D
 

nevets

Jedi Knight
Country flag
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somewhere in Dave's detailed and excellent suggestions, he did mention to check the fan belt tension, which is where I would start.
 
OP
S

SDJHAWK

Freshman Member
Offline
Thank you both, I have already checked the generator via the above instructions and its output is in good. I have not checked the belt though. I may not have reinstalled the generator with the correct tension so I will check it tomorrow. Do you know what the appropriate deflection should be for the belt? I know that upon the generator's reinstallation, I was at between 1/8 and 1/4, but it may have increased over time. Thanks for the suggestions.

Matt
 

Keoke

Great Pumpkin
Country flag
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Hi SDJHawk, the correct deflection on the belt is 1/2".---Keoke
 

higgins

Senior Member
Country flag
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Unfortunately I don't have the same technical experience like Dave but for what it's worth, I can only speak about a similar problem that I had and how it was solved.

The ignition light stayed on on my 100/6 as well.
After having checked all of the above mentioned and with the readings being more or less correct, even the professional mechanics couldn't figure out what was happening.

I carried on driving the car and eventually it kept dying everytime the engine got hot (on cooling off it would restart)

As I was removing the engine anyway, I decided to pick up the courage and take the dynamo apart.

On opening the dynamo, it literally fell apart /ubbthreads/images/graemlins/shocked.gif. /ubbthreads/images/graemlins/eek.gif

I was hoping that it would only be the bushes, but the windings and everything else were either rusted, disintegrated, or whatever else may happen to the d%*!$d thing /ubbthreads/images/graemlins/cryin.gif.

I put in a brand new alternator (cheaper and more efficient than a dynamo) and I haven't had any problems since /ubbthreads/images/graemlins/thumbsup.gif.
 
OP
S

SDJHAWK

Freshman Member
Offline
Thank you Keoke and higgins. higgins, I thought that it could be the generator, but I just rebuilt it not mor than a year ago. I know that it would be possible that I screwed it up, but this is the fifth one that I have rebuilt and I do not think that it is the generator. While you were having your problem, how was your output? Also, while outside of the car did you do a field test on the generator, if so what was the result?
 

AndrewMawson

Jedi Trainee
Offline
When you rebuilt the generator did you remember to flash the field winding terminal to the non earthed battery pole to put the residual magnetism the right sense for your earthing setup(ie pos or neg)?

AWEM

AWEM
 

higgins

Senior Member
Country flag
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Hi SDJHAWK,

I honestly don't remember what the output was when it was measured. As mentioned above, even the mechanics couldn't figure out what was going on although they were convinced that it was some sort of electrical fault.

After I'd taken it out of the car, I didn't do a field test but just decided to screw the thing apart. The bits and pieces that fell out resulted in it not being possible anymore to put together.

I took it to a car electrical company specialising in genarators/alternators and the like to have it restored/rewound. I was kindly informed not to bother as it would be more exoensive repairing it than getting a new one.

Just one small note, are you sure your bushes are making the proper contact?

regards

Higgins
 

bighly

Jedi Knight
Offline
I have a good generator with fresh brushes, It has been polorized to negative ground (easily reversable).
Make me an offer via private mail. I was going to put it up on eBay but have been too lazy.
 

higgins

Senior Member
Country flag
Offline
Hi Bighly,
thanks for the offer but I've converted mine to an alternator.

/ubbthreads/images/graemlins/cheers.gif

Higgins
 
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