Ok so this is my 6th T but most of the ones that I have had before are 24 and up. This part was mounted to the firewall of my 1918. Still had wires attached to it but they were not connected to anything else. I think it has to do with the horn but you guys probably know better.

So what is this?

Headlight dimmer unit.

The non-starter/generator cars from about 1918 (actually clear up to at least 1926!) had a "dimmer coil" because the rpm of the motor powering the headlamps varied the voltage between too dim to see anything all the way up to blow the bulbs. So they altered the light switch to offer both bright and dim positions, then ran the dim side through a voltage dropping coil so as to not blow the bulbs. For a couple years only, the dimmer coil was mounted on the firewall, like the one you show. About 1920, the dimmer coil was moved to the dash mounted switch panel behind a blanking plate where the electrics cars had the ammeter.
The earlier Ts with electric lamps but before the starter and generator, did not use a dimmer coil. For 1915/'16/and at least part of '17, if you drove too fast at night, you probably would just blow the light bulb.
Kind of difficult to say which was worse. A single choice switch with a wide varying voltage? Or a two choice switch and having to switch it up and down every time you raise or lower your rpm? But, Ford wasn't trying to make the non-electrics cars easy after 1918.

That is a fairly rare part! 45 years in this hobby, and I have only seen a few of them. Try to find it a good home! (Preferably on a restored firewall with the equally rare steering column mounted light switch!)
Drive carefully, and enjoy, W2

Wayne, actually the juice goes through the coil in the bright setting too, just not through all of it, so it's the perfect accessory to any 1915-17 T, since it helps the bulbs to last much longer in an intelligent way - the coil cuts the AC voltage spikes without reducing much of the mag juice at lower rpms (ok, it's still not much..)

Is that original Ford or after market?

It's original Ford. Used on all cars 1918 and the open cars most of 1919, then only the non electric open cars that were sold up through 1926. TT's were also often non electrical, so the coils were used all the way through 1927 on many TT'S.

The Forum is a great place to learn about T's. This thread is a good example. I really enjoy learning new things about the T.........

Non-starter/generator tourings and roadsters did not get an instrument panel until the 1922 model year according to Bruce McCaulley's info. The ignition switch remained on the coil box through 1921 for those cars.

The coil was mounted to the firewall when the combination horn button/light switch was introduced in the 1918 and remained there through the 1921 model year.

In 1952, my dad purchased an unrestored non-starter/generator 1920 touring from the original owner. He didn't own the car for very long but it is still in the Twin Cities. I looked at it a few years ago and it has the dimmer on the firewall.

It looks suspiciously like a fragrant mound condensor.

I have wondered what these looked like, so thanks for posting. Your car should also have the fluted horn button which came on these cars (T-6398-A page 69, Snyder's). You still pushed for the horn, but turned the button for the lights, and the internals were different than the common horn button.

The HCCTs have a similar one. The trick is, that with a coil, the higher the AC frequency, the higher the "resistance". That way iy sort of regulate the current through the bulbs so they do not blow. And in the HCCT it will make the reading virtually constant regardless of RPMs so that you can test the magnet with the HCCT (if supported).

Ok so anybody have a diagram showing how it should be wired up? Great info. guys. I need to know what kind of horn/light switch to have I guess or?

Could not find the horn T-6398-a on line but I will dig around in their book.

Thank you Roger K and all for additional clarification! That is what is so great about this site. Many people with bits of information chiming in to make a clearer picture for all. I know that I am still learning. That is why I keep looking back in.

I believe that it is sold, but some good pictures are on this "For Sale" thread of the steering column switch:

http://www.mtfca.com/discus/messages/3487/661091.html?1469465518

There are not enough model Ts restored with this interim system complete and operational. I have never had a really appropriate car for one, and have only seen a very few with a complete working system.
I like this thread! Maybe we can get a few more such cars operational.
Drive carefully, and enjoy, W2

Anybody sell the switch by itself besides Mac's? If so what about quality?

You always Learn something on here. Tim

>That is a fairly rare part! 45 years in this hobby, and I have only seen a few of them<

Has anyone ever unwound a dead one of these and documented the cross sectional area of the laminated core, and number of turns of wire on the core? Just curious...

Got min working well although precarious. Had to solder wires to the existing remnants of wires.

Would there have been one of these on my 1918 TT?

The early ones were mounted to the engine side of the firewall and they had the long wires coming out of them. The later ones mounted behind the ammeter cover plate and those had very short wires coming out of them but the coil itself was the same and only the output "pigtails" were different length. The laminations for the thing were made from fender scrap. As others have stated the thing was a tapped inductor with 3 wires. Each end of the coil was brought out and a tap connected somewhere other than the midpoint of the thing was the third connection.

Forgot to mention that notice it was mounted to the firewall with wood screws and spacers. That was the early version of the mounting and those spacers are the same spacers as used on the coil to mount the points. That was a factory mounting you see pictured there. Later on they made a bracket out of sheet metal and it replaced the 2 spacers.

I have a few of the dimmers for sale, Bob

The spacers were either coil standoffs or magnet supports. Can never remember which; kinda stupid since only one of them will work, obviously.