A friend of mine refers to them as "Stoplight Radios" since you can only hear the radio when you are not moving. 

Tying up loose ends.....

So the black wire was to the capacitor a prior owner had fitted for radio noise suppression..... should have spotted that earlier.... 

dont know now why you need a radio on these cars.... the exhaust note on the pre midget/sprite before they were “socialised” is glorious music enough.... ??

Congratulations!  I am glad you had success.  

She lives........

doug can’t thank you enough ..... brilliant advice and a great education on the workings of sprite ignition systems

many thanks

Rob 

Study the pictures in the two links in my previous post.  The condenser wire and low-tension wire must NOT touch any metal other than the flat spring that is part of the points.  The second site linked above has some very good photographs that show the proper orientation.  It helps to see pictures like those with the real parts.

Awesome info Doug... 

pretty sure I have got the dissy and condenser connectors on top of the insulator washer... will check tomorrow 

Rob 

Do not worry about the black wire.  You said you connected it to the same coil terminal as the white wire.  Therefore, you created a short circuit BEFORE the ignition system components.  You may have damaged the white wire... but your test show it is still providing 12V.  Focus downstream on why the test lamp does not blink when you are cranking the engine over on the starter.

Please go back and watch the video explaining how the points ignition system works.  The coil only produces a high voltage pulse when the points open after the coil has charged up.  Since your test with the lamp across the coil terminals shows the test lamp is always on... your distributor is not breaking the ground connection.  Until you get a flashing light across the coil terminals when cranking the engine you will not get any high voltage out of the coil (no spark).

You have not told us which distributor you have or posted pictures yet.  However, since we now know the condenser wire was removed and replaced I'm going to post a picture link to look at. 

Your engine probably has the 25D distributor on it.  Look at the picture link below regarding the assembly order of the points.  From the bottom up (See the linked picture to understand the numeric references) :
Baseplate with threaded stud pointed up.
Hat-shaped insulating washer (item 5) over the stud... pointed up.
Looped end of points flat spring over the hat-shaped insulating washer.
Then the eyelet on the condenser lead (item 4) followed by the
Low tension lead (item 3).
A second hat-shaped bushing then is installed pointed "down" (item 2)
and finally the nut (item 1).
The low-tension wire (item 3) is the wire that goes over to the electrical connector on the side of the distributor.
The two wires (condenser and low-tension leads) touch each other.
The two hat-shaped insulating washers prevent the two wires and the looped end of the points spring from touching the baseplate (ground). 

It is imperative that you have the hat-shaped washers in the correct places so the two wires and the points spring do not touch ground.  Since you have worked with the condenser, make sure you have the assembly order correct as shown in the picture link below.

Picture Link to 25D Points Assembly.

EDIT:  Also see the page linked below.  It shows in pictures what you have to achieve.  Also... when you get the points working again make sure you do one of the following.  If your points have a felt wick, make sure it is very damp with engine oil.  If there is no wick, be sure to apply some light grease to the 4 lobes of the cam under the rotor.  It is important to lube the 4-lobe cam to slow the wear of the heel block of the points.  NOTE:  If the link below gives you a "not private" warning... just punch through it by choosing "advanced" and clicking that you want to see the webpage anyway.  It's just an old page that has not been updated to the latest standards... it is not a dangerous website.

Link to Picture Explanation of Points Assembly Order.

Hi Doug

i opened the points with a thumbnail! 

I suspect when tried to find a home for the original black wire I’ve done something to the insulation, the connecting plastic tie melted away so the issue may be in there, I did take the condenser lead of and refitting this contacts directly with the connection from the coil... not sure what it should look like.... pretty tricky to get a pic in there, sounds like putting a new set of points on might be a way forward, incidentally although the primary circuit checked out on the tests and the coil check was ok I still don’t get a spark by wiring no4 plug direct to the coil. 

Rob

That says that the coil is getting power from the ignition switch.  Yes, that's good.



What that says is that the points behaving like they are never opening.  They are always supplying a path to ground.  It could be a points problem, a condenser problem, or a wiring problem.

You said manually opening the points leaves the light on.  How are you opening the points?  If you see the points are closed, use a screwdriver to manually lift the insulating heel block on the points away from the 4-lobe cam below the rotor on the dizzy shaft.  The screwdriver must NOT touch the moving metal arm of the points... only that plastic heel block & 4-lobe cam.

If opening the points by using a screwdriver on the heel block fails to turn the light "off" then the problem is likely with the condenser or the connections to the points.

Did you remove and install the points?  If this is a 25D4 Lucas distributor AND you removed/installed points you MAY have put the insulators on in the wrong location.  That will definitely create the "light always on" situation you describe.

Pictures help.  A picture showing the side of the dizzy will identify its type.  A clear picture of the points installed may help answer questions about their installation.

Ok so with test light rigged to ignition side of coil and earth light is on so good?
with lamp rigged to both coil terminals and engine cranked light stays on.... not so good!

so contact breakers are not working properly? Even manually separating the points light stays on 

Rob 

And its worth noting that coils will work when wired back to front ... but just not as well.  This is esp easy if your coil is marked "SW" and "CB" but was originally intended for a + earth car...

And I find the "white wire/black wire" discussion a little dangerous after a few decades.  You need to check what that wire is actually connected to.  Quite a few POs may have paid less attention (Guilty as charged M'Lud) to the colour than to getting the electrons to flow where they're supposed to. 

Cheers, Ian

If you have not ordered your parts yet... don't.  Watch the three Moss videos I linked earlier and carry out their tests.  Coils seldom go bad and new coils tend to be of lower quality than the ones our cars were built with.  Save your money and only buy the parts you need after you troubleshoot the system.

Let us know what happens during the tests.

Hi Doug... so rigged up no4 plug to the coil, first thing to happen was the HT to the coil was pretty crusty and had signs of corrosion to the extent one side of the blades on the cable came away, guessing that didn’t help! Carried on anyway and tried it but still no spark so I’m going to wait till the new leads arrive from AHspares, thought I might as well change the coil anyway cause I suspect the terminal is a bit duff. If that doesn’t work I’ll look at rewiring to the coil and dissy. 

Ill let let you know.

best Regards 

rob 

Good one Doug, I don’t think I’ve ever seen a better explanation of the operation of the ignition system.  

Cheers, Ian

Awesome.... will try this tomorrow 

thanks again 

rob 

OK.  The coil wiring sounds correct.  Don't connect that black wire to anything.

Please don't take offense at the following.  If you are unfamiliar with how the ignition system works, please watch the first of the videos linked below.  After that I have links to 3 troubleshooting videos from Moss Motors.  If you have questions let me know.

Try the videos first, If that doesn't help try the following test and let me know what you observe.  You've been pulling plug #4 and resting it on the block/head while cranking to watch for spark.  That's good but let's eliminate the cap and rotor for a moment.  Pull plug #4 and remove its wire from the dizzy cap.  Pull the high tension lead from the center of the coil and plug #4 spark plug wire directly into the coil.  With the plug resting on a bare metal spot on the head crank the engine again and watch for sparks.  If you see sparks at the test plug during this test then the problem is with the dizzy cap, or rotor, or plug wires.  This is sort of a high-tension version of the 2nd Moss video linked below.

YouTube video links below.
Overview of Points Ignition Systems

Moss Video 1

Moss Video 2

Moss Coil Test

Coil has + & - marks, white wire is on + and white / black on -, the elusive loose black was on the +...

i can believe the dissy has not gone back in the right place but I would still expect to a spark at the plug, albeit it’s firing at the wrong time? I’m checking the spark by taking out one plug... usually no4 and earthing on the block as I turn her over..

i marked the plug leads against corresponding numbers on the rocker cover to make sure they went back ok and i didn’t strip any bits off the dissy when it was out, even left the ht lead in place.
ill try and grab some pics

thanks is for your btw,

rob 

In Lucas wiring, black wires are "grounds".  The coil does not get a ground wire.  When you hooked the black wire up you were probably providing a direct path to ground (effectively making a short).  I'm sorry but referring to coil terminals as top or bottom doesn't help since the coil can be placed in different positions and rotated in its mounting bracket.  Look for "+" and "-", "SW" and "CB", or "1" and "15" next to the coil terminals.  Those are identifiers manufacturers use on coil terminals.

Connecting the black wire can damage wires in the harness but that will not have damaged the condenser.

If the engine ran immediately before your work, you may have done one of the following.
1) put the distributor back in the wrong position (messed up the ignition timing),
2) put the spark plug wires back in the wrong order,
3) broken the carbon brush in the center of the dizzy cap,
4) forgot to put the rotor back on the dizzy shaft.

How are you checking for spark?

Can you post a picture or two of the distributor and coil showing the wires and the routing of the spark plug wires between the distributor cap and engine?

Had the car for years... just fitted new starter solenoid and starter motor because she failed to start,  had to take the dissy off to get the old motor out, not sure I got it back in without something moving although I didn’t turn the engine.. it should still spark the plus though yes?.... the black wire was on the top spade from the coil with the white wire coming off the bottom one... I’ve dismissed it as a red herring because I don’t think it should be there... I did hook it up to the contact breaker for whatever reason!! Caused a bit of smoke so I may have burnt something out ... points look ok, maybe the condenser is stuffed?? 

Motor or spins a treat on the new parts 

Rob 

Never start with blaming the coil.  They do fail but not often and they are the most expensive part to replace.  Troubleshoot first, never shotgun, and check and replace the cheap parts first if they are suspect.

You mentioned you were re-fitting parts.  Did the engine run for you previously or is the car new to you?  If the engine has run for you, what work has been done to the car since the engine last ran (i.e. Did you recently fit new points, dizzy cap, rotor, etc)?

Have you tried to trace back the black wire you mentioned in your first post?