1

TROUBLESHOOTING GUIDE FOR

CAPACITIVE DISCHARGE

(CD) IGNITION SYSTEMS

Most CD boxes operate the same way, making for

common basic test procedures. Most CD ignition

boxes have two separate triggering circuits in them.

One is for a regular points driver signal, which is a

square wave, and one for 2 wire magnetic, which is

a sine wave, and the two have slightly different

test procedures.

Before beginning any testing, start with the basics.

Using your ignition instructions as a guide, recheck all

of the connections and terminals, and make sure the

wires are routed correctly and are free from abrasions

or other damage. Some ignitions also are equipped

with indicator lights that can check the power source

and some internal circuits.

IGNITION BOXES USING SINGLE WIRE POINTS

TYPE TRIGGERING

If the box powers up but does not fire the coil and the

white wire is being used as the trigger source, the

following tests should be done:

1. With the key off, remove the coil wire from

distributor cap and get it where you can jump a

spark to the block, with a gap of about 1/2 inch.

Separate the triggering wire that connects the box

and the distributor together, the wire colors will

differ between boxes and distributor combinations,

for example: MSD, Crane, ACCEL and Mallory

boxes are white. On the Mallory Hyfire I’s to IV’s

and the new Hyfire VI (6) P/N 685, this wire is green.

Refer to your ignition’s instruction sheet to confirm

the color of the wire.

2. Turn the ignition switch to the "ON" position. While

holding the coil wire close to the engine block, tap

the white wire to an engine ground. This will trigger

the box and should fire the coil, jumping a spark to

ground through the coil wire. If there is no spark

from the coil wire and no audible snap comes from

the box, the box is bad. If you hear a snap in the

box but no fire at the coil wire, then the coil or the

coil wire could be bad and they need to be tested.

3. If the test comes out positive and the box, coil and

coil wire are working, the distributor is either not

working or is improperly wired into the system and

the installation instructions should be revisited.

IGNITION BOXES USING TWO WIRE MAGNETIC

TYPE TRIGGERING

1. With the key off, remove the coil wire from the

distributor and position the wire so a spark can be

jumped to the block, with a gap of about 1/2 inch.

Disconnect the 2 magnetic wires from the box and

lay them aside. Next take a short piece of wire and

bend it in the shape of a "U". This wire will be used

to short the 2 wires of the magnetic connector on

the box together.

2. With the key in the "ON" position, the coil wire

where you can jump a spark to the engine block,

and using the "U" shaped wire you have made up,

short the two wires in the connector of the box

together and then disconnect the shorting wire.

3. ach time you disconnect the shorting wire the box

should fire the coil and should jump a spark to

ground. If the coil does not fire then either the

magnetic circuit in the box is inoperative or the coil

or coil wire are bad. Magnetic distributor pickups

are generally 400 to 650 ohms of resistance. If it is

a crank trigger, the pickup is rated at about 80

ohms resistance.

4. With any of the larger MSD, Crane, and Mallory 7

and 8 boxes the tests are similar. The difference is

that they have a terminal strip instead of a wire

harness but have the same two circuits in them

and test as follows.

5. To test the magnetic circuit in the box simply

disconnect the two wire from the "MAG + and

MAG –" terminal on the box. Connect a short piece

of wire to one of the terminals. With the key on and

coil wire ready to jump a spark to the block, rapidly

tap the other end of the short jumper wire to the

other magnetic terminal. The box should fire

the coil.

6. If the trigger is points or Unilite then disconnect the

distributor from the box. Connect a long piece of

wire to the "Points" terminal of the box. With the

key on, rapidly tap this wire to ground and the box

should fire the coil.