Electronic ignition

[DougBGT6]

I'm thinking of fitting electronic ignition, my car is a late GT6 mk3 so it should have a ballasted coil. I've measured it and it's 1.9 ohms which I think is correct for 6v coil. There is no ballast resistor but there should be a resistive ballast wire. I have a diagram which shows the solenoid wire, the dizzy wire and the ballast wire all running to the coil. However I only have two wires. Another diagram shows the ballast wire joining the solenoid wire half way through it's length. So my question is, where is the ballast wire and the join?

[don cook1]

Tony from MGBreakers provides the following:-

AccuSpark â„¢ Help
Coils
One of the most misunderstood and misinformed questions with ignition is
Do I have a ballast ignition ?
And how to test for it ?


First a quick explanation of how a ballast system works
When a car is first started, the oil is thick and the engine is cold and hard to turn, so the starter will draw a large amount of current. Whilst cranking, you may notice the lights dim as the engine turns, this also means that the coil is robbed of current which in turn causes a reduced spark that will make the car hard to start. Often you will find the car starts at the very moment you let go of the key as this is the point it full voltage returns.
To overcome this the ballast ignition was developed. The car is fitted with a coil that runs on a reduced voltage. The coil is then fed through a ballast resistor or wire that reduces the current to the correct voltage for the coil.
Now the clever bit. When the engine is cranking the starter solenoid feeds the coil directly with 12 volts, bypassing the resistor. Although the car is cranking and all the voltage is reduced throughout the electrical system, the coil is receiving more volts than it requires which compensates for the voltage drop, thus giving a full spark.


How to test
Most people will tell you to test the feed for the coil. This tells you nothing - it will always show around 12 Volts because there is no load on the system, the resistor has nothing to resist ! ( unless the points are closed )
If there is no ballast resistor visible you may have a ballast wire inside the loom. To test for it proceed as follows:
Check voltage of battery with volt meter
Remove the wires from the negative side of the coil ( negative earth cars )
Connect a temporary wire from the negative terminal of the coil to earth
Turn ignition on ( nothing else switched on )
Now check the voltage on the coil, put red probe on + side of coil and the - probe to earth
If the reading is less than 80% of battery voltage there is portably a resistor in the system. If it is more than 80% you probably have a standard system
Remove the temporary wire and reconnect wires .
If your reading is less than 80% you should use a ballast coil , AccuSpark Blue 
If you reading is more than 80% you should use a non ballast coil , AccuSpark Red

As a final note :
A standard 12 volt will only have a single 12 Volt feed to coil 
A ballast system should have 2 feeds. One resisted feed and a second full 12 volt feed when the starter is engaged


Do I have the correct coil ? Testing your coil
To test coil set voltmeter to Ohms, test between -and + terminals. A reading of around 3 is a standard coil, a reading of around 1.5 is a ballast coil.
Removing Ballast resistor
What do do if you wish to remove the ballast system and go with a standard 12 Volt system ?

If you have a visible resistor you just need to remove the resistor and join all the wires. 

If you have a ballast wire in the system proceed as follows:

Remove the 2 feeds into the coil and tape up 
You can run a new wire from the coil to the back of the ignition key 
You can also take a feed from the fuse box. This must be switched by the key and be on the live side not the fuse side. To test, it should still work with the fuse removed

Any feedback if this was helpful would be appreciated
tony@mgbreakers.com

[DougBGT6]

Thanks for that Don. I did the test and yes, 6 volts across the coil. So definitely ballasted however, only one feed to the + connector on the coil. So the ballast wire must join the solenoid wire somewhere in the loom rather than at the coil. Most of what I've read says use a 12volt coil with electronic ignition so I'm going to have to find the ballast wire and replace it.

[Dogsbody47uk]

If it helps, the Magnetronic system on y 13/60 has a ballast resistor and the appropriate coil from Magntronic.