Model A

Ford Garage

Distributor Lower Plate Wiring Solution

Pictured above for reference is an NOS lower distributor plate showing the relative positions and orientation of the 3-1/8 inch long wire and flag terminal.

The Problem:

The Model A distributor is frequently maligned due to the unreliable nature of the wiring between the lower plate and the moveable contact point mounting stud on the upper plate.

The original Ford design consisted of a short length of cloth-covered rubber-insulated wire which is crimped and soldered to the bus bar on the lower plate. There was a flag terminal at the other end which was attached with a nut to the stationary post of the movable upper contact point arm.

The rubber insulation on the original era wire is prone to hardening and cracking due to the high temperatures on the top of the cylinder head and inside the distributor casting. This can lead to insulation cracking and a direct short to ground, especially if any moisture is held in the cloth-covered wire insulation.

The chance of insulation cracking is also increased due to the fact that the wire is flexed whenever the spark advance lever on the steering column is moved.

A direct short prevents the primary ignition circuit from 'breaking' and prevents the collapse of the field in the coil (which is necessary to produce the spark). A wire short has the same effect as pushing the pop-out switch to disable the ignition.

Pictured above is a restored original lower plate and two original wire terminal flags. Note the remains of the original high-count fine-strand wire and the original cloth-covered rubber insulation. Most modern automotive wire is even less flexible than the original Model A pigtail.

The shape of the flag terminals is also important. This is the correct shape to mount in the small recess space on the bottom of the upper plate and to avoid contact and ground out with the upper plate, distributor casting, spring, or other ground path. The original Ford design includes the 90 degree bend shown in the flag.

The Solution:

Pictured below is the solution to the heat, cracking, and shorting problems. Shown is an extra-flexible fine-strand tin plated copper ignition wire with silicone rubber insulation.

This type of wire is available in black or red in 12, 14, or 16 wire gauge at most hobby stores that specialize in radio control cars and airplanes.

This specialty wire has very good flexibility and durability compared to regular automotive wire, and the insulation can also withstand much higher and lower temperatures without melting, hardening, cracking or other damage.

The correct overall length of the wire assembly is 3-1/8 inches from the end of pigtail to the end of stationary terminal. Do not make the wire longer than intended, as that will also lead to wire damage and failure. Be sure to carefully solder the wire to the terminal and flag ends to ensure a robust mechanical and electrical connection.

This wire can be used to restore original lower plates, and they will be more robust than any original or reproduction plates, and more reliable than the so called 'wireless' upper and lower plates which can easily develop poor connections in the sliding brass contacts.

I prefer to retain the original design upper and lower plates and points, as opposed to using the so-called modern points and wireless plate.

I also use modern flexible high temperature ignition wire to replace the original cloth-covered rubber wire. This is a very robust solution using modern low and high temperature insulation materials which were not available in 1928.

In addition, it is recommended to also use a modern burn-out proof condenser which can reliably withstand the temperatures inside the cast iron distributor from the nearby exhaust manifold.

More related information on Ford Garage:

  1. For more Model A & B related information, use the Site Search box at the top or bottom of this page.
  2. Model B & Model 46 Distributor Design Details
  3. Model B & Model 46 Distributor Advance Operation
  4. Model B & Model 46 Pertronix Ignitor Distributor Timing Procedures
  5. Model A Remund Pertronix Electronic Ignition Instructions
  6. Model A & B Engine Cam/Valve and Ignition/Spark Timing Discussion
  7. Model A, B, & Model 46 Camshaft Gear Timing Cover Differences
  8. Model A & B Ignition Components Interchange Table
  9. Model A Condenser Capacitance
  10. Model A & B Condenser Details
  11. Model A Nu-Rex Centrifugal Spark Advance Unit

May 2001