RE: Basic Coil 101

["John Fielding" <johnf@domain.elided>]

In the AD today Biba from
Irwindale, CA USA wrote:

>I've always admired those in the electrical / ignition 'know'. I don't
have it, and most likely never will.

>Please help. All I want to know is when I pick up a coil, I want to know
what goes where.

>Please no theoretical lectures, just want numbers.

>I'm sure there must be a kazillion variations, but out of the three
coils I have close at hand, please group the numbers (and yes I'm aware
there's a + in all three which should give me a good hint, but do want
to verify.

>Coil A (Lucas): + & 

+ terminal goes to ignition switch (battery)
- terminal goes to distributor points


>Coil B (Marelli) 1 / D & 16 / B+

D terminal goes to Distributor
B+ goes to ignition switch


>Coil C (Bosch)  /1 & + / 15

Terminal with + sign goes to ignition switch (battery)
other terminal goes to distributor

>Include in each 'group' which is the secondary winding and which is the
primary winding.


The primary winding is the distributor connection AND the supply from the
ignition switch.  The secondary winding is the HT outlet (usually the
heavily insulated and recessed terminal on the top of the coil).


>Now, based on a negative ground vehicle, determine the appropriate
'group' which goes to the distributor.


In practice it makes no difference which way around you connect the
distributor and ignition switch wiring.  However the manufacturers went to
the trouble of marking them to connect in a particular way so I guess they
must have a valid reason to do this?

NOTE:  I am talking here about the "convential canister" coils and not some
of the more exotic encapsulated types which came on the market in later
years!

>Now, based on a positive ground vehicle, determine the appropriate
'group' which goes to the distributor.

The above comments also apply to the negative supply vehicle (positive groun
d),  the polarity of the vehicle has no direct relationship on how the coil
is wired.  The reason is that the secondary winding (the HT) is returned to
the ignition switch side of the primary and hence does not need grounding
externally.  The metal case is isolated from all three connections.  If you
have an ohm-meter you can confirm that point!

However which coil to use on which vehicle is a far more important question.
Without knowing the model number of the 3 examples you gave I cannot tell
what the primary resistance AND MORE IMPORTANTLY what the primary inductance
is.  Both of these are vitally important to get right.  If the wrong coil is
fitted to a Electronic Ignition vehicle the coil and the ECU (spark-box) can
be destroyed.

>Thanking all of you marvelous students in the arcane art (will never
believe it's actually a science) of electricity in advance,

Well ACTUALLY IT IS A SCIENCE, but one which few service technicians
(auto-electrician in particular) seem to trouble with.

John

Durban
South Africa
Alfetta 1.8L turbo

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