Ignition switch question
 

On my 31 A I Have an aftermarket switch IE on or off position. I wonder how this is working? When the switch is off (OPEN) I still get voltage to both sides of the coil. When the switch is on I also am getting voltage. I purchased the car already with this replacement switch in place. When I check the switch with an ohm meter it functions properly (wires disconnected). It also has worked this way since I owned the car for five years. I'm not sure why I am getting voltage when in the off position? What am I missing here?

Re: Ignition switch question
 

What you're seeing is that one side of the circuit is live, but it's not a complete circuit. Current comes from the battery into one side of the coil, wraps around the core a few times, and then exits at the other side. Current goes *from* the coil *to* the ignition, not the other way around. When you check the coil with a voltmeter and touch one lead to ground, you're introducing a ground to the circuit. It will show voltage on both sides because both sides are on the same circuit. Turning the key connects the coil to the distributor, i.e., grounds it. With the key off, it's not grounded (unless you're grounding it yourself with the voltmeter), so no current will flow.

All that is totally normal, that's the way it's supposed to be working.

Re: Ignition switch question
 

Thank you sir for the lesson . Would this be true on any vehicle with a coil or just on a model a that was designed for a pop out switch ?

Re: Ignition switch question
 

The original pop out ignition switch was wired that way. A lot of people wire it differently when moving to a modern switch so that the current flows from the ignition switch to the coil and then to the points. That way the coil is dead when the ignition is off.

Re: Ignition switch question
 

On the Model A, the coil is always hot and the ignition switch doesn't turn anything "on" in the same sense that we are probably more familiar with . The Model A ignition switch just completes the side of the circuit to ground that goes through the points. I cannot answer how other old cars do it, but I believe the Model A was unique.


If you don't have an original pop-out ignition switch, there is a way to wire the switch on the hot side so that you can turn "on" the coil and other accessories, but that will (a) make it not original; and (b) defeat the purpose of anti-theft hot wiring that is part of the reason for the Model A being wired the way it is.

Re: Ignition switch question
 

As said, Most more modern cars are not wired like the Model A. Usually most folks are used to the coil being 'after' the key switch. With an aftermarket switch and the more flexible primary cable the coil can be wired that way.

Its pretty hard to do with the original pop-out switch and heavy original type armored primary cable.

Re: Ignition switch question
 

The armored cable may have stopped some thief in 1930 but today a determined thief is just going to put the car on a flatbed and drive away.

In my car, I have the modern switch and it is wired like a modern car. I have an accessory position which allows me to work on things like the windshield wiper or to program the GPS without having the ignition on. I should note that I have added a distribution block with fuses for the various things, like a modern car. It is mounted with magnets so no new holes were added to the firewall.

Re: Ignition switch question
 

If it's wired from the coil through the switch and on to the distributor as the OEM was then it can be converted if you wish to. The conversion would be to wire the hot side of the coil through the switch then wire the breaker side of the coil direct to the points.

The switch will work either way and can be left as is. The main thing is that the circuit is broken to the ground path so the coil won't be energized if the breaker points are closed. I think Ford did it this way to keep hot wires out of the instrument panel area when the car is turned off and the engine is not running. A hot wire is vulnerable to shorting to ground if the insulation of the wire is compromised and that is not a good thing to happen when the fuel tank is right there next to it.

Re: Ignition switch question
 

Re: Ignition switch question
 

I have pretty much the same thing with one addition: my ignition switch also has a "start" position as well. My distribution block is mounted with Velcro.

Re: Ignition switch question
 

Does anyone have a wiring diagram they could show that shows the coil after the switch to power it down?

I was running new wiring, coil, etc last night and had a helluva time finding the right information for wiring. The wiring diagrams are great but they don't call out the direction of the ammeter ("oh just wire it up and switch it if it's wrong" isn't my style) and everyone kept referencing service bulletins where the wiring was changed to throw the coil in so that its draw would show up on the ammeter.

Now with this information about the ignition and the coil remaining hot, etc...

I would love to see actual wiring diagrams of all these options so I could better understand all these setups. I get it all in theory but I am a visual kind of guy.

Took way too long to wire up everything last night and was made worse by the stellar doc on the MAFCA site that shows some wiring because the ammeter on there has posts reversed for discharge. They call it out in the picture but it didn't dawn on me for the longest time.

Re: Ignition switch question
 

psimet:I hope someone makes a wiring diagram for you. I would like to see that too.

Re: Ignition switch question
 

Most modern ignition coils have a + plus and a minus - marking for the primary terminals. Polarity can be mysterious sometimes but coil polarity testers are are available to make sure it has proper spark. The later coils were connected +plus to the ignition switch power and -minus to the distributor points but they are all negative ground systems. In the positive ground era the -minus would be connected to power and the +plus would be connected to the distributor points but as I mentioned this doesn't always give correct polarity.

This is a link to one of the model A wiring diagrams on Vince's site.
http://www.fordgarage.com/pages/awiringdiagram.htm
It appears to be the last version.

The standard on/off type switch would be wired in similar fashion but no Electrolock.

Re: Ignition switch question
 

..and that one shows the opposite connection on the ammeter.

Kind of like this one in slide 26...
https://www.mafca.com/downloads/Semi...ex%20Janke.pdf

Also shows the Y/BL to the "Charge" side of the ammeter but calls out that the posts are swapped and it's actually the "discharge" side of the gauge as some reproduction units will swap the post sides making them the opposite of the front of the gauge.

The one you just posted shows the opposite with respect to an original gauge that would have the discharge terminal on the "driver's side".

I understand this is DC and a lot of it is just nuances but the wiring diagrams from multiple sources all seem to have variances. The ones that seem like they are the Ford ones don't even list which side of the gauge is which as an example.

Re: Ignition switch question
 

This was posted on Ford Barn in another thread.

https://live.staticflickr.com/65535/...6f2650a5_z.jpg

Re: Ignition switch question
 

Thank you Ruth

Re: Ignition switch question
 

Most ammeters for automotive use have no markings on the terminals. The reasoning is simple. They are made so they will work with either polarity, ie negative ground or positive ground. One side connects to the generator or alternator and the other side connects to the load which is also interconnected to the battery. On more complex systems with higher voltages and amperage capability a shunt or shunt wire is generally used so that it won't overpower the ammeter. The shunt allows the ammeter to read a sample of what current is passing through the cable between the generator or alternator and the electrical buss that all other systems tap their power from which includes the battery storage.

If a freshly installed ammeter reads discharge with a system that is known to be functioning correctly, the leads will need to be swapped on the ammeter terminals so it will read correctly. Ammeters are always connected in series. If a person connects a terminal to ground then it will make a load out of the ammeter and fry it or the wiring.

Re: Ignition switch question
 

*snap, crackle, pop*. :D I get it...I just don't want to button everything up and then have to pull it all apart and swap the wires.

...I'll take the time sometime and think through everything so I can figure out how I want to set it up. Right now really just wanted to do it "the way Henry did it", but there's 2 ways depending on whether I want to do it the way it was new or the way it was changed to in the service bulletins.

Re: Ignition switch question
 

I recently rewired the ignition portion of my 31 coupe. I also was confused by the many different diagrams for the various years of Model A's. I had a car at age 14-21 years and I rewired that car when only 15. I was troubled by the diagrams then too. The diagrams in the link you suggested did not help me either. I humbly suggest they aren't correct, but I'm no expert.

The original 1928 wiring of the ignition portion of the Model A was modified over time. You can refer to the service bulletins for that info, but the final diagram is still a bit confusing because of the representation of the ammeter. When I looked at the diagrams I was mentally viewing the firewall as if standing in front of the car. If the diagram does not show the face of the ammeter with the plus and minus scale, then a novice like myself can be confused as to where to put the two wires that go to the ammeter. If the diagram shows the ammeter face then one is viewing the diagram from the seat of the car! Which is it, dang it!

Yep it's confusing, but you can buy a nice diagram (large) from Snyder's for a few bucks and hang it on the wall. It shows the proper ignition system which evolved over time. The most important change was that earlier car's ignition problems were harder to diagnose when there was ignition trouble.

After a small modification (service bulletin) that moved the power source for the - neg side of the coil from the solid yellow wires, the discharge side of the ammeter, to the + charge side, the yellow with black stripe wires in the terminal box ... the proper opening and closing of the distributor points causes the ammeter to flicker. This flickering instantly tells a mechanic that the points are receiving current and thus pretty much eliminates all the circuitry and components from the battery up to the distributor points as being part of any ignition failure. (whew, that's a mouth full)

Pretty slick huh? Henry moved one end of a short wire and saved a lot of diagnosis time for the Ford dealerships.

The odd thing about the A's ignition for us modern folk is that it is a positive ground system with the ignition switch wired into the ground side of the ignition coil. More modern autos are negative ground, as stated in a previous post, and have their ignition switch wired into the source side of the coil.

I wired my car as the evolved, final diagram shows. And I bought the Les Andrews red service manual from one of the suppliers. Then the ignition trouble shooting method he describes in his excellent manual works like a charm.

Re: Ignition switch question
 

Its nice that Ruth posted the diagram. It should help. And, its nice to learn something every day, I didn't know Ford installed electric fuel valves in any of the 'A's. [ smiley face X2 ].