25 replies to this topic

[Chrome_GT]

Hi Doug,  

I finally got around to doing this check. 

Connect the jumper wire between coil (-) and earth.

Turn the ignition key to "run".  <  -This is where it all went horribly wrong. Upon turning the key to run, I saw smoke, and switched off as quick as i could. The white wire going between the loom and the -ve on the coil started to melt its insulation. Have i had the +ve & -ve wires switched over all this time?? 

Measure the voltage between coil (+) and earth.

If you measure about 12V, the car has wiring for a standard ignition coil.

If you measure 6V to 9V, the car is wired for a ballast coil.

Edited by Chrome_GT, 03 July 2015 - 11:08 AM.

[Chrome_GT]

Also:

My white wire was on my -ve coil terminal

My White/black wire was on the +ve coil terminal

Oh dear this isn't looking good.

[KernowCooper]

Coil wires back to front, White is coil + and White/black is coil -, so the white wire has melted its insolation correct? thats because it was a dead short to earth, is the wire completly melted or just got hot enough to smoke ? you may be looking at putting in a new White 12v wire. Its checking to ensure its not melted between fusebox take off, to the coil area in the loom. its take off point is fuse 1 top left hand side when viewed from the front of the car. Any doubt renew it.

Edited by KernowCooper, 03 July 2015 - 10:48 AM.

[Chrome_GT]

Hi Dave, There are a couple spots on the white wire where i can see copper. I don't know what the condition is within the loom.

 

If my wires were reversed, then how did the car manage to run at all?  It took a lot of cranking and crc 'jump start' to get it to fire but after that it would run. Is it possible for the car to run with those wires reversed? 

[Chrome_GT]

A couple extra notes.

I can confirm that the Coil on it's own tested 4 ohm across it. It also says on the coil it is a 12V coil. 

I have a single white wire coming from the loom

I have a single white/balck wire coming from the loom

I am questioning my statement above regarding having the wires switched. Maybe I mistook this in my panic after seeing smoke (I started disconnecting everything frantically) 

[Chrome_GT]

I guess there are a few  scenarios now. Please do comment on these as I welcome your thoughts, opinions, even insults

 

1: I had the wires the correct way around. Then why did i cook my white wire. I added jumper between the -ve coil terminal & the the earth strap on the gbox bellhousing. I then turned my ign key to the on position. Saw smoke, switch off again.If the coil is cooked inside, does that lead to short circuiting? The coil got hot yesterday as i left my key on 'run'  for a while without the car running.

 

2: I had my wires back the front. How would i have managed to get the car to even run if that was the case. If it is possible it'd be interesting to know. I've looked at this website and it appears it could be possible http://mgaguru.com/m...ition/ig104.htm

Edited by Chrome_GT, 03 July 2015 - 11:18 AM.

[KernowCooper]

Ok if your coil wires were correct and you place a jumper to earth on the coil- then the resistance of the primary winding acts like a bulb in a circuit but in this case the coil gets hot but does not get hot enought to glow like the bulb, no wires burn out feeding the coil.

 

Incorrect wiring the coil - is a direct short to earth as it has 12v on it, just the same as if you took the coil White 12v and put that to earth

 

Yes the car will run with the  coil wires back to front, the effect is poor running / starting and in one of my course book from Lucas I did they show a section there if you reverse the coils wires incorrectly, the result is the spark is reversed as the electrons like to leave a hot point of the plug the centre electrode and jump to the cooler earth electrode, so wires reversed the spark is reversed with a loss in spark of 35-50% the Coil in effect sucks the spark rather then pushes the spark out if that makes sense?

[Chrome_GT]

Thanks Dave. Yeah makes sense and also describes the very poor starting I was having for the last three years +.

Tomorrow I'll repeat the test doug described above; With the wires in the correct position. Just a last check to confirm I'm wired for 12v non ballasted. I'm tempted to give the car a good charge and then see I it starts ok. The white wire probably didn't melt enough to cause major drama but
I am thinking I should disconnect that white wire at both ends and run a new wire outside of the loom. Does the wire need to be anything special if I am a pure 12v non ballast case. I have plenty of decent speaker wire I could use.

[dklawson]

Sorry I missed all these posts.  You and Dave have been busy!

 

As Dave said, the engine will run with the coil wires "backwards" but the spark is much weaker.  

 

Replace the melted wires.  If the damage is severe, you may want to peel the loom open and inspect adjacent wires to make sure the white wire did not ruin them when it overheated.  As a minimum, run a new white wire to the coil.

[KernowCooper]

Normal speaker wire is to thin, use the normal colour White wire.

 

A 12v Coil with a 3ohm Resistance will draw 4amps and will be 48watts

 

You could use 0.5mm 16/0.20mm -(11amp)  but I prefer to use 1.0mm 32/0.20mm.(16.5amp) to feed coils with

[Chrome_GT]

Thank you. I'll go buy a small role Of that wire as it'd be proper to make sure the colour is right too. I'll have a closer look at the loom today.