The Ford Barn

Tom Wesenberg · 04-22-2011, 11:48 AM

Model A Ignition System

The Model A ignition system consists of the battery, amp guage, ignition switch, coil, distributor, spark plugs, and wires connecting these parts. A failure in any part means no spark to the plugs.

The coil always has 6 volts at the primary terminal and the coil is connected to the points when the ignition switch is turned on. The popout switch in the OFF position grounds the points, so the distributor contact on the popout cable should show continuity to ground and the coil terminal (by the key end) should show no continuity to anything. In the ON position the distributor contact should show continuity to the coil terminal, and neither terminal should show continuity to ground.

Repro switches are simple OFF-ON single pole switches with no connection to ground. The main fault I find in repro switches is the contacts in the back of the switch are not a very positive contact and often don’t make a good connection.

When the car doesn’t start, check the simple things first. Pull the coil wire from the cap and hold it ¼” from a head nut while cranking the engine with the key on. You should have a good blue spark. If you have a weak yellow spark check the points and condenser first. Condensers are very easy and quick to change if you follow these steps exactly.

1. Have the new condenser laying 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. To check the function of the points, stop the engine with the points open and key ON, then short the points contacts off and on using a screwdriver. If this produces a good spark, then the points need to be cleaned. If you are getting no spark, but the coil is getting hot, then something is grounded between the points and coil, which keeps the coil turned on full time. Be sure to oil the distributor often.

The Model A coil primary consists of 250 turns of # 20 enameled wire. The coil secondary consists of 16,000 turns of #38 enameled wire. The condenser is .3 mf.* See page 390 in the SERVICE BULLETINS for a change in the coil connections. 1928-9 coils have the negative terminal on the passenger side, while Nov. 1929 and later coils have the negative terminal on the driver’s side. Date codes can be found on the coil mounting bracket.

When checking cylinders for power, it’s better to SHORT the spark plug, rather than to disconnect the plug wire. When the spark has no place to go it tries to find the easiest path to ground, which may be to jump internally inside the coil to the metal body, or arc at the coil tower.

1928-9 slant pole coils have the metal case around the primary terminals, so make sure the first thing to go on the terminal studs is an INSULATING WASHER, then a flat washer, lock washer, and a hex nut. Barrel nuts are used to secure the wires to the slant pole coils. NO boots are used on the coil wire.

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. If you do a Google search on “COIL POLARITY”, CHICAGOLAND MG CLUB has an excellent short article about checking spark plug polarity and why it’s important. Check:
http://www.chicagolandmgclub.com/tec...neral/574.html

* Thanks to Vince Falter for the coil and condenser information.

This is the sheet of notes I handed out last night at our club clinic when I gave a talk about the ignition system. This applies to the original ignition system and parts. More notes can be added, especially for after market parts, such as: some aftermarket coils are oil filled and must be mounted with the tower facing UP.

Feel free to add to the list of notes if you can think of something I missed.

04-22-2011, 11:48 AM	#1
Tom Wesenberg Senior Member Join Date: May 2010 Location: Mpls, MN Posts: 27,582	The Model A Ignition System Model A Ignition System The Model A ignition system consists of the battery, amp guage, ignition switch, coil, distributor, spark plugs, and wires connecting these parts. A failure in any part means no spark to the plugs. The coil always has 6 volts at the primary terminal and the coil is connected to the points when the ignition switch is turned on. The popout switch in the OFF position grounds the points, so the distributor contact on the popout cable should show continuity to ground and the coil terminal (by the key end) should show no continuity to anything. In the ON position the distributor contact should show continuity to the coil terminal, and neither terminal should show continuity to ground. Repro switches are simple OFF-ON single pole switches with no connection to ground. The main fault I find in repro switches is the contacts in the back of the switch are not a very positive contact and often don’t make a good connection. When the car doesn’t start, check the simple things first. Pull the coil wire from the cap and hold it ¼” from a head nut while cranking the engine with the key on. You should have a good blue spark. If you have a weak yellow spark check the points and condenser first. Condensers are very easy and quick to change if you follow these steps exactly. 1. Have the new condenser laying 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. To check the function of the points, stop the engine with the points open and key ON, then short the points contacts off and on using a screwdriver. If this produces a good spark, then the points need to be cleaned. If you are getting no spark, but the coil is getting hot, then something is grounded between the points and coil, which keeps the coil turned on full time. Be sure to oil the distributor often. The Model A coil primary consists of 250 turns of # 20 enameled wire. The coil secondary consists of 16,000 turns of #38 enameled wire. The condenser is .3 mf.* See page 390 in the SERVICE BULLETINS for a change in the coil connections. 1928-9 coils have the negative terminal on the passenger side, while Nov. 1929 and later coils have the negative terminal on the driver’s side. Date codes can be found on the coil mounting bracket. When checking cylinders for power, it’s better to SHORT the spark plug, rather than to disconnect the plug wire. When the spark has no place to go it tries to find the easiest path to ground, which may be to jump internally inside the coil to the metal body, or arc at the coil tower. 1928-9 slant pole coils have the metal case around the primary terminals, so make sure the first thing to go on the terminal studs is an INSULATING WASHER, then a flat washer, lock washer, and a hex nut. Barrel nuts are used to secure the wires to the slant pole coils. NO boots are used on the coil wire. 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. If you do a Google search on “COIL POLARITY”, CHICAGOLAND MG CLUB has an excellent short article about checking spark plug polarity and why it’s important. Check: http://www.chicagolandmgclub.com/tec...neral/574.html * Thanks to Vince Falter for the coil and condenser information. This is the sheet of notes I handed out last night at our club clinic when I gave a talk about the ignition system. This applies to the original ignition system and parts. More notes can be added, especially for after market parts, such as: some aftermarket coils are oil filled and must be mounted with the tower facing UP. Feel free to add to the list of notes if you can think of something I missed. Last edited by Tom Wesenberg; 04-22-2011 at 11:55 AM.