Assistance required !

[stevests]

I'm a "T" guy helping a buddy with a '29 A with a repro 3 terminal ignition switch - key goes left & stays in the cylinder, key in center is removable & key to the right it stays in - small armored cable is attached to left terminal, nothing on center & red wire to coil on right - coil is hot at both terminals - can anyone assist in straightening me out ?

[J Franklin]

Use one or the other.

[Patrick L.]

Coil terminals on an A are both hot. If battery is + grd then + coil terminal should go to grd.[points] thru the switch. The switch is only used to power/unpower the points.

Some switches have 2 positions, some 3 as for an accessory.

[Bob C]

To add to what Patrick said. The coil will be hot on both terminals if the points
are open but only on the black wire if the points are closed.

[nkaminar]

The left position is accessories and runs everything except the ignition and a fuel pump if that is installed. The position on the right runs all the accessories plus the ignition. Accessories can be plugs for a GPS, fog lamps, a radio, etc. The accessory position can power things like the head lights instead of them being hard wired. The right position is hooked to the ignition coil if the wiring has been modified, see below.

Your best bet is to remove the wires from the switch then use an ohm meter to check the functions of the switch. Then sit down with a piece of paper and draw out the circuit diagram by tracing the wires to see where they go. The stock Model A wiring had the coil hot all the time and the switch connected the coil to the points. A lot of Model A's have had the wiring changed over the years. Some people feel it is safer to have the coil not hot when the ignition is off so the ignition switch supplies power to the coil only when it is on and the other side of the coil goes to the points. Do not assume anything, trace all the wiring. They hook up the switch the way you want it.

Since the accessory position is on when the key is turned right, that key position connects the red coil wire to the armored cable that goes to the points. This duplicates the function of the original pop-out switch. The center position or left position of the key will kill the ignition. (This all assumes the accessory-off-ignition positions of the switch.)

A good site for all things electrical is: https://www.mafca.com/downloads/Semi...ex%20Janke.pdf

[stevests]

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Much appreciate the help fellas ! I had a '30 Coupe 50 years ago & forgot about the "hot" coil - thought it was peculiar back then !!!

So, I'm asking if no accessories present, which wire goes to the center switch terminal ?

[rotorwrench]

The coil has power connected to it but it's only "Hot" when the circuit to ground is connected in the form of closed points.

The system can be modified to be more like a conventional ignition system when a conventional ignition switch is utilized. Connect the wire that is for the distributor breaker direct to the ➕️ side of the coil then run a power wire from the main ignition output to the coil ➖️ terminal. This will require a power wire from the load side of the amp meter to be connected to the battery terminal on the switch. Most model A cars don't have mutch for accessories. The dash light and a windshield wiper if so equipped are about it. Some cars have a dome light and some don't. The 3 brush generator doesn't allow much for extra power usage.

[nkaminar]

To run the modern switch like the old style pop-out switch, run the wire from the coil, I think it is red, to the center, and the wire in the armored cable to the side of the switch that is electrified when the switch is turned to the right. Make sure you have an aftermarket fuse that mounts next to the starter switch because if the back end of the modern switch shorts out to the tank or dash it can cause a fire without the fuse.

See https://www.snydersantiqueauto.com/p...6199&cat=41746

The original wiring on the Model A was an anti theft method. The pop-out switch grounded when it was not on (popped out) which meant that you could not hot wire the distributor. The armored cable prevented the wire from being cut and could not be unscrewed from the distributor without removing the distributor. Today this is not much of a problem as most people don't know how to start a Model A and thefts are almost unheard of, except if someone puts a car in a trailer to steal it.

[stevests]

Thanks again fellas - I should get her going now !

[rotorwrench]

Actually the pop out opened the circuit to prevent a ground pathway for the ignition breaker points when the switch button was pushed in. When the switch was popped out, the grounding circuit pathway was completed so that the points could control the function of the coil.

[nkaminar]

Rotorwrench, You are correct in that when the switch is popped out it connects the coil to the points and in effect creates a ground path through the points when they are closed. However, the wire that goes to the points (armored cable) is disconnected from the coil and grounded to earth when the switch is pushed in. See http://www.santaanitaas.org/wp-conte...anti-theft.pdf