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Are
You Resisting the Resistance Check?
The Mallory Ignition
E-Spark, Crane Cams Fireball XR-i, and the Pertronix Ignitor
all call for verification of the Ford loom resistance wire
or proper ballast resistance in the wire between your ignition
key and the positive side of the coil before installing any
of their respective units. In fact, the manufacturers not
only call for verification, they SCREAM it judging by the
emphasized instruction sheet warnings. However, opinions about
how this test should be performed differs between the various
manufacturers, tech support, and sometimes between the same
manufacturer's installation literature AND tech support. Between
studying instruction sheets and making many calls to the tech
lines at Crane Cams, Pertronix, and Mallory, I made a gallant
effort to sort it all out for you in this section. Before
I get started, here's some background on the forms of ballast
resistance found in relevant ignition systems.
Proper resistance in the wire between
an ignition key and the positive side of the coil can come
in three forms. A ceramic ballast resistor, a loom
resistance wire (wire with "internal" resistance),
or a matched coil with
additional "internal" resistance built-in. I say
"additional" because
every coil shows some resistance across the negative and positive
poles.
Usually in the 1.0 to 1.5 ohm range. Coils with additional
resistance will
usually be in the 3.0 ohm to 4.0 ohm range. Testing your coil
is the first
test anybody should perform before installing a points-to-electronic
ignition conversion kit, especially if the coil is unlabeled
or out of
production. I show it here on the bench but this can be done
in the car
as well. Just be sure to disconnect all leads going to the
coil terminals.
As Ford owners, we are in luck because
most Fords originally equipped with a points-style ignition
came with a "loom resistance wire". In theory, this
means that the hassle of purchasing a high resistance coil
or adding a ballast resistor is not required for any points-to-electronic
ignition conversion kit. However, when using a points-to-electronic
ignition conversion kit you should check your coil to ensure
you are not adding unnecessary resistance to your system by
performing the test shown above. With a loom resistance wire,
a coil with 1.5 ohms of resistance is optimum.
For the sake of this article, I acted
as if I did not know my test vehicle had a loom resistance
wire and conducted manufacturer
dictated tests on a 1973 Ford Gran Torino referencing instruction
sheets
and tech support. I got started with the Crane Cams Fireball
XR-i.
Verification
of a Ballast Resistance Wire According to Crane Cams
This is the test as specified
by the Crane Cams Fireball XR-i Ignition
Instruction sheet:
You can determine if your vehicle
has external ballast resistance with
this simple test. Disconnect any wires going to COIL (-).
Reconnect battery.
Turn the ignition on but do not try starting the engine. Use
a voltmeter
and read voltage between COIL (+) terminal and ground. It
should be about 12 volts. Then momentarily jumper COIL the
(-) terminal to ground. If voltage at COIL (+) drops below
8 volts, there is ballast resistance
between the ignition key and the COIL (+) terminal.
I performed Crane Cams' test on a stock
ignition and this is what I
came up with:
 
As expected, voltage between the COIL (+) terminal and
ground was almost 12 volts.
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With the jumper connected to
COIL (-) and then grounded, the meter not only read below
8 volts, it was below 6 volts! Keep in mind, I had already
added a low-resistance 1.3 ohm coil. |
Although I had just confirmed the existence
of a loom resistance wire, was the voltage drop far enough
below 8 volts to raise concern of too much resistance? To
validate my concerns, I inquired with Crane Cams technical
support. Surprisingly, the representative I spoke with denounced
the test scripted within the instructions, calling it dangerous,
and advised I use this simple test:
Start your car and bring it up to
a fast idle, around 1500 RPM. First,
record voltage at the battery. Next, record voltage at the
positive side
of the coil. For optimum ballast resistance, you should have
a 1.0 to 1.5
volt drop at the positive side of the coil. A voltage drop
greater than
1.5 volts suggests too much resistance. A voltage drop less
than 1.0 volts
could burn out the spark module when installed.
Here are the results of Crane Cams' adjusted
test on our stock ignition:
With the engine at 1500 RPM, voltage across the battery
terminals registered at 14.29 volts.
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Reaching across to the positive side of the coil, voltage
read 9.59 volts. Another large drop in voltage |
The adjusted test suggested by the Crane
Cams tech still confirmed that my loom resistance wire was
producing too much resistance for optimum
operation.
Verification of Proper Ballast
Resistance Wire According to Pertronix:
The test for proper ballast resistance specified by Petronix
tech support
is the same as the test found in Crane Cams' Fireball XR-i
Ignition
Instruction sheet. Yes, that's the same test denounced by
Crane tech
support. The only difference is that Petronix asks for a reading
very
close to 8 volts with no range specified. When asked about
checking
voltage at the positive side of the coil with the car running,
Pertronix
tech support responded that this will not yield an accurate
reading therefore it is not recommended.
Sticking to the parameters of the Pertronix
test procedure, I confirmed once again that my loom resistance
wire was producing too much resistance for optimum performance.
Verification
of a Ballast Resistance Wire According to Mallory Ignition:
The test as specified by the Mallory E-Spark Instructions
are very similar to the verbal test offered by Crane Cams
tech support, only Mallory suggests that the test be taken
at idle, not 1500 RPMs. Here is the test per the E-Spark instruction
sheet.
One easy way
to find if your vehicle has a loom resistance wire is to test
your stock ignition system voltage while the engine is at
idle at the COIL
(+) terminal. If the measured voltage is within 1-volt of
battery voltage,
an ignition ballast resistor must be installed in the wire
from the
ignition switch.
The results of Mallory test procedure
confirmed the existence of a loom
resistance wire. Like the other manufacturer's suggested testing
procedures, this test showed the potential of compromised
spark strength by having too much resistance.
Final thoughts
on Ballast Resistance Verification
If you are already running a points-to-electronic ignition,
there's a good
chance you skipped the section on verifying proper ballast
resistance
prior to installing your kit. Fortunately, for most Ford owners
this
inaction will not result in a prematurely burnt-out spark
module because most of us have a loom resistance wire. With
that said, the question you should be asking yourself and
the manufacturer is...
"Can my
Ford loom resistance
wire be providing too much resistance?"
Interestingly,
despite results showing "excessive" resistance in
my
ignition system, all three kits appeared to operate perfectly
once
installed. Crane Cams, Pertronix, and Mallory Ignition provide
ample
precautionary information on how to prevent burning out their
spark modules with too much voltage. As an enthusiast looking
for optimum performance however, I was left looking for more
information on how to maximize voltage to coil (+) without
compromising the spark module.
To satisfy my own curiosity, I bypassed
my loom resistance wire. While I cannot confirm this is a
proper setup, my voltage at Coil (+) improved without causing
a threat to a spark module.
This didn't feel too good but what the heck, it's just
a FordMuscle test mule. I identified the ignition wire
at the ignition switch, snipped it, and added my own wire.
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This was the smallest ballast resistor I could find. A
Mopar .25 ohm resistor. |
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I installed the resistor inline within the new ignition
wire. |
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With the car idling I had 10.31 volts at 1500 RPMs. Performing
the jumper test with the car off but ignition on, I achieved
6.75 volts. |
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