IGNITION BALLAST RESISTOR AND/OR CONDENSOR/CAPACITOR
by Lorne Goldman & Ted Bridge

This can be a very frustrating issue for British cars fit with an ignition coil and distributor. Most Morgan Plus 8s (overseas excepted) were fit with distributors until 2000.
A.  Foreword
B.  Understanding a Ballast Resistor
C. Testing a Ballast Resistor
D. Advantages and Disadvantages of a Ballast Resistor Over a Capacitor/Condenser
E. Condensor Capacitors
F. A Third Possibility on Later Morgans and LRs.

FOREWORD
I have now run across three instances of a bad capacitor or ballast resistor in Morgans up to the point their ignitition systems began to use coil packs (circa 1996-2002 from a faulty memory). If I am noticing that fault cropping up..it is the time for an article. It is very difficult to diagnose. The symtoms are varied:
1. The car can run for 20 minutes or so, but then stalls, Only restarting after a rest. if you are lucky This is because the coil is overheated and its internal oil is boiling.
2. The car will run unsteadily. This is because;
a: The lack of one (ballast resistor or condensor/capacitor causes a too high voltage to run through the coil and the distributor, damaging the coil (which will become EXTREMELY HOT) and the distributor cap
3. The car will overheat.

Understanding a Ballast Resistor 

A Ballast Resistor is an electrical device that reduces voltage to the coil so that more energy is available for the spark plugs during starting. Its resistance increases as current flows through it is increased and its resistance reduces as current flows through it drops. As a result, a device that helps to preserve voltage stability. This added stability increases ignition and running stability. Additionally, their usage reduces the chances of coil failure by reducing coil voltage and current, ensuring that the coil does not overheat as a result of the addition. An overheated coil quite often causes damage to distributor and its amplifier. The high heat of a over-heated coil also increases engine bay temperatures to sad effect.

Traditionally, ignition systems didn’t use a ballast, meaning that the ignition system used a 12v coil with a 12v feed from the battery via the ignition switch. This system is fine when the engine is running. However, it can be problematic when starting because the starter motor draws a huge amount of current from the battery, leaving the ignition system and the spark plugs with less energy to create sparks. This is mad worse during colder starting temperatures or when the starter motor is worn, requiring even more energy for the starter motor and leaving less available for the spark plugs.

To counteract this distribution of energy, ignition systems were changed to use a 9v coil instead of a 12v coil. A 9v coil gives the same output as a 12v coil when provided with a 12v feed, resulting in a better spark for starting with less energy draw on the starter motor. Once the engine is running, the 12v feed is cut and the coil continues to run on the 9v feed.

Which coil should I use if my car has a ballast resistor?

Use a 9 volt coil. Never try to run a ballasted coil when a ballast resistor is not present in the ignition system! 

N.B. There ARE internally ballast resisted coils. Mallory coils with red tops are one
such coil. However, I do not recommend them. In fact, neither did Mallory! The
reduced power expresses itself in extremely high temperatures on the coil body,
enough to burn your skin. External Ballast resistors are inexpensive and reliable,
most often encased in ceramic to resist high temperatures.  Here are reviews of
the best. 		SIGNS OF A  FAILED BALLAST RESISTOR
N.B. WATCHPOINT  Rover used a odd ballast resistor for a
short period (1980 to 1981) before junking it as unreliable. It
consists of a plate mounted behind the coil. Part #  
DAC2043 IT IS NOT ADVISABLE TO USE IT.  
  • Premature ignition coil failure.
  • Weak or no spark at the spark plugs.
  • The voltage coming out of the resistor matches the voltage coming into the resistor. Use a voltage meter or multimeter to diagnose this problem.

Testing a Ballast Resistor

To test the ballast resistor in automotive applications an ohmmeter or a multimeter is needed.

If the ignition coil is not linked to the ballast resistor, the ignition coil receives the entire supply voltage. The battery is usually utilized to power the ignition system. The battery voltage will most likely be 12V in most circumstances. If the voltage level decreased to 7-8V after connecting the ballast resistor, then the ballast resistor will be in good condition. However, if the voltage level of the ignition coil will be high it means the ballast is damaged. So, to extend the life of the ignition coil we need to lower the voltage and for this purpose we connect a ballast resistor to the ignition coil to decrease the voltage. Test for voltage at the power entry side..should be 12+Volts. Now test for voltage at the end wired directly to the positve side of the coil. It should be lower.
 
Ballast Resistor in a LED Circuit

The LED bulb may be damaged if the source voltage in an LED circuit is higher than the rated voltage of the LED bulb. To avoid this, a ballast resistor should be connected in series with the bulb. The voltage across the LED is decreased to a safe level by connecting the ballast resistor in this manner. 

Advantages & Disadvantages

1.  These resistors assist in the regulation of voltage and current in electrical systems.

2. This resistor safeguards the coil, the amplifier and the distributor from overvoltage and overcurrent.
   
3. In the rest of an electric circuit, these resistors diminish variations in current and applied voltage. As a result, a ballast resistor is mostly utilized for over-voltage, current, or protection inside various automobile and light circuits in order to provide circuit stability.

4. Maintenance. None. They should last forever

5. A disadvantage is that with a ballast resistor you may need Radio Frequency Interference (RFI) Suppression spark plug wires as without them your sound system may have static. However, almost all new spark plug wires are Radio Frequency Interference (RFI) Suppression except very cheap ones.

Cost & Availability  10-20 British pounds. Available at any auto store in the world.

Capacitor (aka a Condenser)
Understanding Ignition Capacitor/Condensers

Though the end result is the same.  However, rather than being wired in series and reducing the battery voltage before it reaches the coil as a ballast resistor does, a capacitor /condenser DRAWS voltage from the positive (+) coil post! for a moment before releasing it

Maintenance. They should be changed every 2 years as they will fail without a warning sign. As noted above, they will then proceed to damage your distributor and its amplifier. They are even cheaper than ballast resistors, costing a couple of £s at most.  Sadly, Land Rover used them for a short period on LR and Morgan Plus 8s until they learned better. Frankly, the best idea to avoid inevitable sadness is to replace them with a ballast resistor. A one-pint job. Here is an excellent article more fully detailing the curse of a Lucas igntion coil condensor/capacitor.

Way of Testing a Capacitor Condenser

TEST ONE. 1.) Remove the condenser from the engine (or at least disconnect the lead wire). Note the small metal connector located on the end of the condenser. This connector is the "hot" or power connection. The metal case of the condenser is the grounding point. Discharge the condenser by shorting the lead wire to the case.

2.) Switch the meter to the ohms position. Place the red lead into the "ohm" connector on the meter. Insert the black lead into the "com" or common connector on the meter. Set the resistance range to the highest available setting (if it is selectable). Connect the test leads together and zero the meter. If the meter won't zero replace the battery. (Yes, an ohm meter has a battery).

3.) Touch the red lead to the hot connector on the condenser. Place the black lead to the metal case on the condenser. The meter's needle should jump slightly to the right (toward 0-ohms), then should drop back to the left towards infinite resistance). Hold the leads in place for 15 to 20 seconds. This action places charge in the condenser. If the test shows any reading other than infinity, the condenser is leaking and needs to be replaced.

4.) Remove the leads and reverse the placement to the condenser. Move the red lead from the hot connector to the metal case, and move the black lead from the metal case to the hot connector. At the moment where both leads are touching the correct points, the meter should jump towards the right. The second time the needle may move twice as far, as this action discharges the condenser. Holding the leads in contact should again result in movement of the needle back toward infinite resistance.

5.) Movement of the meter's needle indicates the condenser is good. If no movement was indicated on the meter in any circumstance, the condenser is bad and must be replaced. Retest the condenser several times for a consistent reading.

In operation the condenser will "ring" at up to 300 volts, so the condenser/capacitor needs to be rated much higher, no less than 600 volts DC. The ignition will likely work with any capacitance value between 0.05 and 0.6 microfarad. Too high or too low value may eventually transfer metal from one side of the contact points to the other side leaving a pit and a point. Capacity of spark coil capacitors ranges from 0.2 microfarad to 0.33 microfarad. Almost all automotive coils use a 0.25-0.29 microfarad capacitor.

A capacitor may absorb moisture over a long period of time, and moisture will cause failure of the condenser. So it is possible that a condenser stored for 10 years or so might be bad or might fail prematurely in service. It is a good idea to check your traveling spare condenser occasionally.

TEST 2 Video

WATCHPOINT. The logic here is merely mine. The advantage of it is that it works. I have had much success helping my brethren with it. Good Luck!

A THIRD POSSIBILITY I have run across another LR/Morgan set-up. It is a INTERNALLY ballast resisted coil, a DUCELLIER from France. These to not require either a ballast resistor or a condenser/capacitor. I ran two Plus 8s with Mallory internally ballast resisted coils for a year. I stopped when Mallory confided THEY did not like them! You have a two common sense options to avoid sadness when travelling:
1. Buy a Decellier internally resisted coil and carry it in the car

2. Switch to a ballast resistor and a decent coil of any type you can find anywhere in your mogging area.