Re: [OMC-Boats] Wiring questions

From: Lee Shuster <lks@...>
Date: Wed, 17 Jun 2009 09:15:17 -0600


Sometimes electrical terminology gets confused with thermodynamics
terminology. I'm going to assume when you use the term "HOT" you mean
thermally, not (necessarily) presence of electrical potential
(voltage) although it sounds like both may possibly be present.

Let's also clear up some other terms. An engine can be not running,
(as in it just stalled) while the helm-mounted IGNITION switch is
still in the ON position. The original OMC Ignition switch has OFF -
ON (RUN) - START positions.
Note: Unlike most automotive applications, there is no ACCESSORY
position on this switch. You can retrofit a new switch if you want to
run electronics or other devices with the motor not running.

NEVER Leave the IGNITION SWITCH in the ON position when the engine is
NOT running. The ballast resistor and coil will heat up under normal
operating conditions, but you risk damage and failure leaving the key
ON with the engine not running. Also with the switch ON, if your
sterndrive was out of water and in gear (forward or reverse)
additional current would flow to the clutch coils and generate excess
heat in the lower unit. At the very least you'll potentially drain
down and discharge a marginal battery and not be able to raise or
lower your power lift or start your engine. And we know how much wives
or significant others love that!

I've never taken ballast or coil temp measurements after prolonged
(normal) usage, but I would imagine they will be quite warm. But
here's what's more important: The resistor and coil WILL cool off
rapidly when you shut the IGN SW OFF.
So do that check, as well as the the other checks I've listed below.
There should obviously be no voltage present with the IGN SW in the
OFF position at the coil or ballast resistor.

Here's a couple of factory OMC wiring diagram you can reference (both
wired identically, just different wiring color schemas depending on
age of your boat):

I can't tell from you description if your boat has been re-wired or
mis-wired. On the POS (+) side of the coil, one (red) wire should
trace back to the ballast resistor and measure about 6 - 8 volts with
the IGN Switch ON. The other wire should be RED/WHITE STRIPE and it
should run back to the starter solenoid. It should measure 12-13 volts
only when the SWITCH is in the START position.

This additional info may help you/others to better understand why
Ballast Resistors are sometimes used in Coil-Points Ignition systems.

There are many misconceptions about ballast ignitions and what they
do. Up until about 1955, most vehicles used 6-volt systems. When the
switch was made to 12-volt system, higher compression V8 engines were
putting greater demands on ignition systems. Some bright engineer got
the idea that a hotter spark could be provided using existing 6-volt
coils. The full 12-volts is "temporarily" provided for "hotter"
staring spark, and then the coil is returned to operated on 6 to 8
volts during normal running. The ballast resistor is what reduces the
12-14 volts essentially in half. If you know Ohms law you do the math.

The ballast ignition system includes an external resistor in series
with the voltage supply to the coilís (+) terminal. A internal
resistor coil will have an internal resistance close to 3 ohms on its
primary windings. The coil for a ballast ignition system (As on OEM
OMC boats) will have a primary winding resistance between 1 and 2
ohms. The external ballast resistor will typically provide an
additional 1.5 - 2 ohms of resistance.

Current flowing through the ballast resistor will create a voltage
drop and thus lower the coilís operating voltage to something between
6- and 9-volts.

Together, the ballast resistor and the internal resistance of the coil
limit the current flowing through the system. The coil in a ballast
ignition system will have a second connection on its (+) terminal.
(sometimes these are joined on the ballast resistor, rather than the
coil) This second connection is from the starter solenoid. During
cranking the coilís (+) terminal will receive full battery voltage.
This produces a MUCH hotter spark to help the engine start. Once the
starter is released the coil receives its power through the external
resistor which drops its operating voltage to the 6 - 9 v range.

The ballast coil can thus produce a hotter spark for starting.
However, if the ballast coil is wired into the ignition system WITHOUT
the external resistor it will always operate at high voltage. The
increased current flow through the system and the higher spark
voltages will cause premature failure of the distributor points. It is
imperative therefore that the proper coil be installed to maximize its
ignition system reliability and life. When troubleshooting a ballasted
ignition system the external resistor and its associated wiring must
be added to the components to examine.

It is important when buying a replacement coil that the correct type
is selected for the ignition system to achieve acceptable life and
performance. Old boat ignition systems are often modified over the
years and determining what is required may not be as simple as
referring to the ownerís or service manual. Visual checks should be
performed first. Externally ballasted ignitions use a ballast
resistor between the ignition switch and the coil (+) terminal
(frequently RED or sometime PURPLE/BALCK in color). The ballast
resistor will typically appear as a small ceramic brick (with wires)
mounted in the vicinity of the coil itself and connected between the
ignition switch and coil (+). Ballast ignition systems also have a
wire between the coil (+) terminal and the starter solenoid.

If the boat's electrical system is totally unmolested these visual
clues may be enough to identify the ignition coil type installed/needed.

To confirm the needed coil type it is best to make electrical
measurements with a volt/ohm meter. Start by measuring the resistance
across the coilís low-tension terminals with all the wires
disconnected. Note this resistance value but do presume it correctly
identifies the coil needed. Perform the following additional test: Re-
attach the low-tension wires removed to perform the previous test.
Connect the volt meter between the coilís (+) terminal and chassis
ground. Temporarily fit a jumper wire between coil (-) and ground. The
jumper wire will insure that current is flowing through the coil and
any ballast components during the test. It is necessary for current to
be flowing to correctly measure the coilís operating voltage. With the
meter and jumper wire connected, switch on the ignition and observe
the meter. If the meter shows battery voltage (nominally 12V), the
system is non-ballasted and needs a standard (internally ballasted)
ignition coil. If the meter displays anything between 6V and 9V, a
ballast-type ignition coil is required regardless of what type of coil
is currently on the boat. Internally ballasted ignition coils will
have a primary resistance close to 3 ohms, while externally ballasted
ignition coils are typically between 1 ohms and 2 ohms. Using a
standard (internally ballasted) coil on an externally ballasted
ignition system will result in low spark voltages potentially leading
to running problems. Using a ballast-type coil on a standard ignition
system (without an external ballast resistor) will result in excessive
current flowing through the ignition system. This will cause premature
wear of the points and potentially lead to reduced coil life.

Lee Shuster

On Jun 16, 2009, at 8:47 PM, jd wrote:

> Two different mechanix have messed with my wiring and even though it
> started/ran yesterday, things don't seem right....
> 1) what is the ballast resistor for and is it supposed to be 200+
> degrees when engine is off/cold? I'm guessing no. Both terminals
> light up my tester when grounded.
> 2)is coil supposed to be hot when engine Is off/cold?
> 3) neg terminal of coil has black from distributor, and grey from
> tach. Pos terminal of coil has red from distributor and red coming
> from one of ballast resistor's terminals.
> Other ballast resistor has purple coming from looks like ignition.
> Thanks!
> _______________________________________________
> OMC-Boats mailing list
> OMC-Boats@...
Received on Wednesday, 17 June 2009

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