One of the most misunderstood
and misinformed questions with ignition is
have a ballast ignition ?
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
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
If you reading is more than 80% you should use a non ballast coil , AccuSpark
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