3 questions about lights, horn ammeter

[bmklawt]

I have a 1927 Touring, I here talk about magneto lights and battery lights, may I assume if I have battery lights they only work when the switch is in the battery position and vice versa for the mag lights. I don't see in the schematic how to hook up mag lights, I don't want these, just curious.

How do I tell if I have a mag or battery horn.

What is the most basic way to test that the ammeter is working when out of the car.

[RajoRacer]

The headlight switch has no bearing on electric or magneto lights - they're on or off with the lever switch - not the key switch.

Magneto horn has a quite small backend whereas the electric horn's is quite large in comparison.

Someone else might describe ammeter testing.

[Steve Jelf]

1 Unless your car came from the factory without a starter, you have battery lights. Only non-starter cars have mag lights. The MAG/BAT settings on the switch are only for which runs the engine ignition, not the lights.


2 A mag horn has an adjusting screw in the center of the diaphragm. A battery horn doesn't.


3 Attach lead wires to the ammeter and run current from a battery through it. Trading terminals at the battery ends of the wires, the ammeter will show a charge or a discharge.

[Ron Patterson]

The wiring diagram you posted though electrically will work, but is not physically correct. There are many Model T wiring diagram floating around and most of them have errors.
This wiring diagram depicts problems that are part of very commonly misunderstood five wires in the Model T Ford charge and discharge circuits and will result in slightly dimmer headlights and the ammeter will not show a discharge when the horn button is depressed.
Some will say I am being too picky, but I learned the hard way. Many years ago when I first started helping folks with Model T electrical problems I was invariably told by the owner "the car is wired correctly" only to find out later it was not. Most of the problem centered upon those pesky commonly misunderstood five charge/discharge circuits wires. As far as I am concerned the car should be wired as it came from the factory; if for no other reason than to prevent confusion when future trouble shooting.
I refuse to help anyone with wiring problems

19-27 Wire Harness Wiring Diagrams.pdf

(245.87 KiB) Downloaded 71 times

unless they agree to use a wiring diagram I know for a fact are correct.
This is also why Bob Cascisa and I set out to make a set of wiring diagrams for Model T's that were absolutely correct.
Attached (last page) is a the correct wiring diagram you should be using when wiring and trouble shooting a 1926/27 Model T equipped with the FA starting and lighting system.

[TRDxB2]

Reference the link for the proper diagram and save it for future reference.
The ignition switch is actually two switches in one.
The key determines the source of power, inner ring, MAG OFF BAT. The handle operates the outer ring for lighting DIM (low headlight filament & tail light) ON (high headlight filament & tail light). The ammeter is an indicator of current flow, and not very accurate. With the engine off turning on the lights should cause the reading to go minus -, how much depends on the amperage of the bulbs. That's indicating that the power is coming from the battery. With the engine on and lights off the ammeter pointer should be showing a positive value +. That indicates that the power is coming from the generator. If you look at the 1926-27 wiring diagram and trace the wire from the magneto post to the terminal block,2, to the switch - nothing else is connected. When the switch is turned to MAG (or BAT) it completes the connection to the COIL position.
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Note how the yellow & yellow traced wires connect to the outer BAT screw and a jumper connects to a second screw (used to power the coils). This allows for the lights to operate independently of he engine running