Ignition Basics

Inspection: When moving the Spark Advance Lever inside the cab, all the way up and/or all the way down, the spark retard arm on the distributor should not make contact with the Upper Distributor Body on either side. The fix: For the 29-31 two tooth steering, loosen both steering column clamps. One is inside the cab and the other is under the hood. Rotate the steering column until the arm functions properly. Tighten the clamps.
Inspect the Distributor Shaft. The Distributor Shaft should not rock back and forth. If it does rock, it is time to replace the bushings.
	Slight rotational play is ok.
Setting Rotor/Distributor Contact Gap
Put on parking brake, place gear shift lever in neutral position, and use the Hand Crank to rotate the rotor. Check the rotor at all four distributor contact points. The gap should be .025   The fix: Bend the Rotor and/or file the contacts on the Distributor Housing.
Setting Point Gap To adjust points proceed as follows: 1. Lift off distributor cap, rotor, and body. Turn engine over slowly with hand crank until breaker arm rests on one of the lobes of the cam with the breaker points fully opened. 2. Loosen lock screw and turn the contact screw until the gap is between .018 and .022”. A standard thickness gage is used to obtain this measurement. When correct adjustment is obtained, tighten the lock screw. After tightening the lock screw, again check the gap to make sure the adjustment was not altered when the lock screw was tightened. 3. Replace distributor body, rotor and cap or proceed to ignition timing.
Ignition Timing: 1. Inspect the Distributor as stated above. 2. Put on parking brake 3. Place gear shift lever in neutral position 4. Fully retard spark lever. 5. If not previously done, remove the distributor cover and lift off rotor and distributor body. 6. Check Point Gap. If necessary adjust them as previously described above.
7. Screw out timing pin located in timing gear cover and insert opposite end of pin into opening. 8. Find Top Dead Center. With the hand crank, turn the engine over slowly, at the same time pressing in firmly on the timing pin. When piston # 1 reaches the end of the stroke (top), the timing pin will slip into a small recess in the cam gear. Tip: If the engine had been running recently, the timing pin should drop into the recess when the rotor is about to line up with contact #1 on the distributor cap.
Note: While hand cranking to find the timing mark mark, occasionally pause to relieve the compression pressure. Note: If the timing mark is missed it is two revolutions, with the hand crank to return to the previous point. Note: By removing Plug # 1 and shining a small flash light into the hole, it is possible to see the top of the piston when you are at Top Dead Center. Note: By removing all the plugs, the compression is eliminated and the engine is easier to hand crank.
9.Remove the cap and rotor. Loosen cam locking screw until the cam can be turned. Note: A cam wrench can be purchased from one of the Model A venders, makes the job easier. 10. Replace rotor and/or use the cam wrench to turn and line up the notch in the cam with the No1 contact point on distributor head. 11. Remove rotor and/or wrench from cam and using your fingers slightly turn the cam in a counter clockwise direction, until the breaker points are fully opened. 12.Slowly turn the cam back in a clockwise direction until the points just close.
13. Lock the cam by securely tightening the cam locking screw. This method removes the backlash in the distributor shaft from affecting the timing. 14.Turn on the ignition and with your fingers twist the cam counter clockwise. With the slightest movement the points should spark. If it does not spark retime. Final check with the ignition on pull the spark advance lever down one or two notches and listen and/or have someone watch for a spark from the points. If the lever moves more then three notches retime. Replace timing pin and put away crank Oil the distributor and Apply Vaseline to the cam. 15. Reassemble distributor housing, rotor, and cap
Model A's are positive ground. The Model A frame acts as the positive ground wire from the battery
The Primary Circuit. The primary circuit is the low voltage circuit that controls the ignition system. Battery - provides the power to run the system. Ammeter - Used to measure the current flow. Ignition Switch - allows the driver to turn the system on and off. Points - a mechanical switch that acts as the triggering mechanism to break the circuit to collapse the magnetic field in the coil. Condenser - provides a false ground and protects the points from burning out. Primary Coil - produces the magnetic field which collapses and creates the high voltage in the secondary coil. Wires - join all the components together. Model A Frame - acts as the positive wire used for ground.
The Secondary Circuit The Secondary Circuit is the high voltage side of the ignition system. The voltage is generated when the magnetic field collapses in the primary windings. Secondary Coil -Creates a high voltage when enacted upon by the collapsing of a magnetic field in the primary coil. .Coil Wire - a highly insulated wire, that takes the high voltage from the coil, to the distributor cap. Distributor Cap - a plastic cap with an electrode to distribute the electricity to the rotor. Rotor - spins around on the top of the distributor shaft, and distributes the spark to the right spark plug. Plug Connectors- metal strip that takes the high voltage from the cap to the plugs. Spark Plugs - Highly insulated electrode that forces electricity to arc across a gap in order to ignite a fuel air mixture in a combustion chamber of an engine.
Primary and Secondary System The ignition switch allows the driver to turn the system on and off. Turning the key to the on position closes the circuit and allows current to flow. As current flows around the primary coil, a magnetic field is created. The strength of the magnetic field is determined by how long the points are closed. The points act as a mechanical switch that is controlled by the distributor's cam. When the points open, the circuit is broken; this instantly collapses the magnetic field and induces a high voltage into the secondary windings. The voltage is so intense that in its path to ground, it is able to ionize the air gap of the spark plug, thus igniting the fuel air mixture in the combustion chamber.

How The Condenser Works The function of a condenser is to provide a false ground. When the points open and the magnetic field collapses in the coil. A high voltage is created in both the primary and secondary windings. The voltage in the secondary windings heads towards the spark plugs to ignite the fuel; while the new induced voltage in the Primary windings searches for ground. The voltage created by the collapsing of the magnetic field in the primary coil is strong enough to jump the gap between the points in the distributor as they open, but instead, the current is attracted to the condenser, where it is collected and stored to assist in the next cycle of creating a magnetic field in the Primary Coil.
Note: At one time the condenser was considered the weak link in the system and failed often. Today's reproduction condensers do not fail like their predecessors and are quite reliable.
Tom Wesenberg Tip: "Condensers are very easy and quick to change if you follow these steps exactly. 1. Have the new condenser lying next to the distributor. 2. From the passenger side, remove the ground screw FIRST. 3. From the driver’s side remove the condenser terminal screw and be sure to keep light pressure on the screw while you slip out the old condenser and slip in the new one. 4. Tighten the terminal screw, then go to the passenger side and tighten the ground screw. Always set the points to .020” first, then set the timing. Remember that the points setting can affect the timing, but the timing can’t affect the points setting. Be sure to have lube on the points rubbing block. I always carry a small piece of sandpaper in my billfold just in case I need to clean points, or check an engine number at a swap meet, etc. A points file is good to keep in your car’s tool kit and only costs about a dollar."
How The Coil Works The coil itself does not care which way it is hooked up, it will be just as efficient either way. On the other hand the spark plugs do care. They prefer the center electrode to be negative and the end electrode to be positive. The reason is electrons like to jump from a cold surface to a hot surface and the center electrode of a spark plug is hotter than the end electrode. By correctly establishing the coil’s polarity the voltage required to jump the spark plug gap is 15 to 30 percent stronger which may or may not be evident on the performance of your ‘A’ depending on the condition of the ignition components. Oddly enough the large amount of voltage created by the coil is not affected, positively or negatively, by the mere 6 volts (or 12) of the battery. Therefore; positive ground or negative ground of the battery is not relevant.
Tom Wesenberg Tip: "To check coil polarity hold a pencil lead in the spark path with the plug wire about a third of an inch away from the distributor terminal. You’ll see a FLARE on one side of the pencil lead and this flare should be on the spark plug side of the lead." Tom suggests to hold the pencil in the middle or even slide the pencil into a plastic tube to avoid an electrical shock. If the flare is on the plug wire side. Switch the two wires on the coil.
Restoration Tips by Tom Endy
Distributor Techniques Numerous articles have been written concerning the rebuilding of the Model A Ford distributor. Just about any one of them will get you through the rebuilding process. The intent of this article is to provide some tips to help you do the job better.
Distributor Roadside Seminar On any long club tour sooner or later one of the Model A's will pull over to the side of the road and up will come the hood. The first component to be attacked is the distributor, and it is probably the most likely source of the problem..
Model A Ford Ignition Diagnostic Ammeter "Jiggle"... A wealth of knowledge:
The Ammeter The ammeter in a Model A Ford can be a very useful tool in a variety of situations that will signal to the driver the car’s electrical status.	Source:  http://modelabasics.com/Ignition.htm

Coil Polarity

I was converting my older Euro car over from positive to negative ground when I came across the question of coil polarity. I discovered coil polarity is very much misunderstood. In researching it, I was very confused until I found out there are two definitions of coil polarity. I talked to three or four knowledgeable people on the subject and read several technical books and articles. Everything made sense in itself but didn't jive together until I found out they were talking apples and oranges.

Definition #l Coil Polarity (In relation to battery)

The polarity of the coil should match that of the battery by connecting it so (+) goes to (+) and (-) connects to (-). But don't worry about which way you install the battery (positive or negative ground) or which way you install the coil (regardless of coil markings) it will automatically adjust itself. The coil will work efficiently and put out the same voltage either way it is hooked up, but the spark plugs are more sensitive when it comes to polarity, hence our second and more important definition.

Definition #2 Coil Polarity (In relation to spark plugs)

Coil polarity should be such so as to provide negative polarity to the spark plugs center electrode.

It has been found that it takes approximately 15% less voltage to form an arc at the plugs, if the hotter center electrode is negative, and the cooler (by comparison) ground electrode is positive. The center electrode is hotter since heat transfer from the tip must make its way through the porcelain insulator past the sealing gaskets to the shell block and then to the water jackets.

If your center electrode is positive, your car will probably still run fine until, with its 15% handicap, it exceeds the coil output. If you live where temperatures dip down to 0° you may not get your car started. Driving with a full load and accelerating hard up a hill may cause an ignition miss. If your ignition system is well worn to where you have various voltage losses, you could get a miss.

Correct coil polarity won't eliminate these problems, just put them off by 15%.

If your coil has - & + markings by the primary terminals, you will be pretty safe by hooking it up by those marks, but test it for correct polarity anyway, using one of the tests listed further on. If your coil has CB & SW or BAT & DIST markings, there is no way of telling if the coil was marked in relation to a positive or negative ground car, and the only sure way to tell if the coil is installed right is to test it out.


You test for correct polarity by hooking up a voltmeter with the negative lead to the plug terminal (which should be of negative polarity) and the positive lead to the block (which should be of positive polarity). Set the meter on the highest volt range. These connections remain the same whether you have a positive ground or negative ground electrical system. The secondary winding's polarity which we are testing is determined by the combined hookup of the battery and primary windings, so it may or may not match the battery's ground.

Cranking the engine over (you don't have to start it) should show an upward swing of the voltmeter needle (don't be concerned with taking a reading). If the needle swings down off the scale, your coil is hooked up wrong. To correct, reverse coil primary leads. Do not worry about the coil markings (refer to definition #1).

If you don't have a voltmeter, test by removing a plug wire from a plug and hold a plain lead pencil point in the path of the arc. A flair (hard to see) towards the plug shows correct polarity while a flair towards the coil shows reversed polarity. 

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Ford Barn Thread:

Original Post:  

In the Model A Ford Mechanics Handbook by Les Andrews, shows the  Black wire from the coil connecting with the Yellow/Black Tracer wires on the driver's side terminal of the box. This would then be routed by the Yellow/Black Tracer to the Ampmeter charge side and to the generator cut out. The instructions here seem to  be helpful because they identify "drivers" or "passengers" side.

*In the original Ford service bulletins, the Black wire goes to the terminal with the Yellow wire connections ( Fig 444). This would be routed to the Ampmeter discharge post and the Starter Motor

terminal. No mention of drivers or passengers side.

Also, my coil is a slant pole and does not indicate which side is positive and which is negative (drivers or passengers side would be really helpful here). Les Andrews says the red wire from the ignition switch should to the positive coil post. Therefore, the black wire should go from the negative coil post to the Ampmeter / Generator terminal post which would be Yellow / Black Tracer??

Can anyone shed some light on this wiring contradiction? I have thoroughly confused myself. But the two diagrams are clearly different.

Response #1:

Either wiring will work. The only difference is that one will make the ammeter needle twitch a little bit when you turn the key on and crank the engine (because the power going to the coil from the battery has to go through the ammeter). The other will not make the needle move because the current is taken from the battery before the ammeter.

I like having the ammeter needle move a little bit when I turn the key on and crank. It confirms that the points are working. To do that, take the power feed for the coil on the generator side of the ammeter, not the battery side.


Response #2: 
If you look closely at the Service Bulletin on the wiring change you will see that with the slant poll coil you need to crisscross the black wire from one side of the coil to the opposite side of the terminal box. This changes it for the ignition to read through the ammeter while retaining proper polarity of the slant pole coil.

Response #3:
If you read the service bulletins you will see that a change was made to the ignition circuit to pick up it's power after the amp meter. I have no idea why the original design had the ignition circuit not flow through the amp meter.


Response #4:
About the same time Ford switched sides for the feed wire, they switched coils from slant pole to straight pole. To add to the confusion Ford switched polarity on the coil posts when they switched the wiring to run the coil through the ammeter. However, a few slant pole coils were made with the polarity the same as the new straight pole coils. So, on ALMOST all slant pole coils, the driver's side is the red wire, which leads to the switch, then points, and is the POSITIVE side.

See page 390 in the Service Bulletins. If you have any questions about coil polarity, check out what is posted by the Chicagoland MG club:  http://www.chicagolandmgclub.com/tec...neral/574.html

I did the same as Jim and moved my slant pole feed wire to the other terminal, so the drain would show on the ammeter. Now while the generator is charging, the ammeter shows ONLY the amps going into the battery, where the original way it showed the amps going into the battery, plus the amp or so to run the slant pole coil.

Response #5:
Also, after the latest specified Model A Ford wiring changes, it was recommended to connect all additional Model A electrical items to the Driver's Side Terminal of the fire wall terminal box; however, "if" one obtains & installs "Logo Lite" turn signals, the Logo Lite manufacturer recommends connecting their Logo Lites to the Passenger Side Terminal of the fire wall terminal box.


Source:  http://www.chicagolandmgclub.com/techtips/general/574.html
Source: http://www.fordbarn.com/forum/showthread.php?t=89736