MTFCA Forum

I am currently restoring a 1922 Model TT that I purchased as a basket case. I've run into some confusion regarding wiring the coil box.
With the switch on the dash and the motor having a starter, how do I wire the magneto post and the battery post? Am I correct in my interpretation
that i wire the bottom bronze strip in the box to the magneto post and leave off the battery post? Most of the info I can find on line deals with coil boxes with integral switch. Any help would be greatly appreciated.

Someone will post a wiring diagram. There are 3 connections on the back of the switch. One goes to the strip at the bottom of the coil box. One goes to the magneto, and the other one goes to the battery. When the top of the key is turned left, the connection is made to the battery, when the key is straight up and down the ignition is off, and when the top of the key is turned right, the connection is made to magneto. These connections must be correct so that the coils either run on battery or on magneto, but the magneto is NEVER connected directly to the battery.
You can start the engine on battery, and it will run on battery as long as the top of the key is to the left. To switch to magneto, you must turn the key fast so the engine does not kill. Do not switch from battery to magneto while the engine is pulling. Make the switch to magneto at idle. Even if you forget to switch and realize it when driving along, you can quickly go to neutral and reduce the throttle, then quickly make the switch to mag and release the pedal as you increase the gas. If you make the switch while in gear at a fast speed, you might blow the muffler.
Norm

Griff47 wrote: ↑

Tue Sep 13, 2022 11:11 am

I am currently restoring a 1922 Model TT that I purchased as a basket case. I've run into some confusion regarding wiring the coil box.
With the switch on the dash and the motor having a starter, how do I wire the magneto post and the battery post? Am I correct in my interpretation
that i wire the bottom bronze strip in the box to the magneto post and leave off the battery post? Most of the info I can find on line deals with coil boxes with integral switch. Any help would be greatly appreciated.

Here are some diagrams that should help
Its sounds like you are referencing this diagram for wiring to the MAG post vs the BAT post. This diagram is for Coil Boxes with the ignition switch mounted on the box. But yours is mounted on the dash so its different. Even though this shows the switch plate for a 1926-27 the wiring is the same for the rectangular switch plate --
The coil box wiring is pretty much the same for all starter cars. Coil boxes with the ignition switch mounted on the box use two bottom posts on the coil box for input (MAG & BAT). Dash mounted ignition switches use just one post that gets its input from the "coil", center connection, on the switch backing plate. Here is a wiring diagram

This is how the switch on the box is wired. Included for those who misread the question like I did.

Besides the wiring diagrams that the forum members have posted for the wiring you also need the Ford service manual that’s available from the parts suppliers. You will need it to get a grasp of the Model T Ford engine and Transmission and how it functions. I would also contact the parts suppliers for their parts catalogs.
They are a great resource for their diagrams of parts, identifying them and what goes where.

Remember this is 100 year old technology and not quite like todays computerized cars.
Try to learn the ins and outs with the magneto, mag ring, spark coils. You will definitely need to know WHAT NOT TO DO when you work on them and the rest of the engine.

Good luck!

Griff47 wrote: ↑

Tue Sep 13, 2022 11:11 am

I am currently restoring a 1922 Model TT that I purchased as a basket case. I've run into some confusion regarding wiring the coil box.
With the switch on the dash and the motor having a starter, how do I wire the magneto post and the battery post? Am I correct in my interpretation
that i wire the bottom bronze strip in the box to the magneto post and leave off the battery post? Most of the info I can find on line deals with coil boxes with integral switch. Any help would be greatly appreciated.

There appears to be confusion on what coil box and ignition combination you have so a picture of the switch or box front will resolve that.
Here's why
With the switch on the dash and the motor having a starter,
then you added Most of the info I can find on line deals with coil boxes with integral switch.
So some are focused on an integrated switch & coil box

Your '22 should have the later coil box with just a single terminal on the right, below the 4 ea. plug terminals. That single terminal is wired to the lower strip or common, in the bottom of the coil box. The '26-'27 box on the right, that terminal is just a machine screw under the bottom of that style box which mounts on the engine.

That terminal spot is where you run the blue/tracer wire from the switch loom...to the 'coil' terminal on the back of the panel switch. With that post wired to 'coil', when you turn the ignition key to BAT or to MAG, the corresponding + source, either DC volts from battery or AC volts from Magneto go to the coil box to electrify the coils to fire by the timer, which the rotor does by grounding the 4 timer segments in the timer case.




Note wire to the coil terminal on switch from the post on the coil box.

I think the one you should use is the one Dan Treace posted. I have a 22 with the switch inside on a dash panel and that is how it is wired. What Dan's diagram calls a distributor is commonly called a timer. If you have stock T ignition system you would have a timer.
Norm

Norman Kling wrote: ↑

Tue Sep 13, 2022 4:18 pm

I think the one you should use is the one Dan Treace posted. I have a 22 with the switch inside on a dash panel and that is how it is wired. What Dan's diagram calls a distributor is commonly called a timer. If you have stock T ignition system you would have a timer.
Norm

The one Dan posted is the same as the one I posted (so lets not confuse thinking that they are different). I explained that the the Rectangular & Oval switch plates are wired the same for starter cars. Non-starter cars are wired entirely different and a different schematic is needed. Both of our diagrams show the coil wire going to a single post.
So here is an attempt to show the difference in wiring a dash mounted ignition switch to a coil box vs an ignition switch mounted on a coil box
There is are versions for non-starter dash ignition switch and dash ignition switch to '26 -'27 coil boxes
The confusion comes from the the coil box bottom that is grooved for both methods.