The Stovebolt Site Forums The Shop Area The Electrical Bay 1955 foot start and ignition questions

Hello.
Two questions
First.
Im trying to understand how ignition works on a 1955 second series truck. Foot start. ignition switch is Off/On. I think I understand, so im looking for confirmation or correction.

Im looking at the wiring diagram in the 1955 second series shop manual.

Three wires are shown going to/ from ignition.
20g Violet from resistor bypass in starter to start on key.
20g Dark Brown from key from ign 1through resistor to + coil.
20g Dark Green from ign 2 to splice between resistor and + coil.

As I understand it.
you turn on key and push the foot start. This engages the starter. power is sent from the resistor bypass terminal through the violet wire to the start on the key. this power then goes through the Ign 2 green wire to splice then to + coil, bypasing the resistor.
Once you remove your foot from the starter switch, power to the coil now comes from Ign 1 brown wire through the resistor to + coil.

These sequences alow full 12v at + coil during startup and reduced current at + coil while running.

Do I understand this correctly?

Second question.
Since the ignition switch has 4 ACC terminals on the back, Im currious how many amps the switch is rated at?

I understand how to use relays to reduce the draw on the switch. Just currious about the switch.

Thanks for the help.
Rock 49

The bypass circuit through the ignition switch prevents the engine from running momentarily if the starter pedal is pushed with the switch in the off position. It's a safety factor, not a potential overcurrent situation. Without the bypass circuit going through the ignition switch, the engine would be able to run anytime the start pedal was pushed, intentionally or not. It's an early version of the neutral safety switch and/or a clutch switch on later models.
Jerry

Jerry,
Thanks for the safety note regarding the by pass circuit. So within the ignition switch the start termunal and Ign 2 are connected to facilitate by passing the resistor during start.
This prevents accidental start with key off while alowing a full 12v to coil during start.

Now I have a better Idea of whats going on and why its the way it is.

Rock49

The key start engines with points and a resistor also have that "ign 2" terminal built into the ignition switch, which serves the same purpose. There is a "R" terminal on the starter solenoid cover that provides the full battery voltage to bypass the resistor. I spent 30-something years teaching auto mechanics, including point-type ignition systems. Most Delco-Remy ignition coils operate on about 9.5 volts, so they need the resistor to drop the 14-something volts from the charging system down to prevent point burning. When the load of the starter motor is on the system, most batteries drop to 9-10 volts while cranking. The low voltage coil primary assures a good spark during cold starts.
Jerry

Jerry,
So the voltage drop is to protect both the coil and the points.
I have a 66 F100 that I replaced a wiring harness in 20 years ago. I had issues with bad coils and points fouling. I couldnt figure out what was wrong so I parked it. From what you told me it looks like I need a resistor or resistor wire installed into the ignition system. Now I know. From curiosity on how a chevy ignition system works to a posable solution for a problem I gave up on years ago. Cant wait to see if adding a resistor does the trick.

Thanks for the knowledge.

Mechanical points can carry a maximum of about 5 amps without burning. The resistance of the coil primary winding is the main control of primary current, but the relationship is not a straight function of Ohm's Law. As current flows through a coil of any sort, there is an initial surge of amperage that's almost a "dead short" situation, followed by a rapid buildup of "inductive reactance"- - - - -an opposition to current flow created by the buildup of magnetic induction in the windings of the coil. Simply measuring the resistance of a coil winding will not give an accurate estimate of the current it flows, since at 2K RPM, for instance, the coil is being turned on and off approximately 100 times per second. Lots of "higher mathematics" are involved in engineering an ignition system, but it can all be made a moot point by simply installing the wrong coil. Most Ford systems do not use a ballast resistor- - - -they simply accept the lower voltage during starting. Old Henry Ford didn't trust his engineers very much!
Jerry

But Henry Ford was gone before Ford cars/trucks had 12 volt systems.

True- - - -but his insistence on a minimalist approach far outlived the man himself. Without venturing too far out into the weeds in this thread, I can cite several examples of that corporate mindset that plagued Ford for a long time after Henry was out of the picture.
Jerry

So, inspired with my new knowledge, i dug into the 66 wiring schematic. no balast resistor. there is however a resistor wire in the ignition circuit. Could this resistor wire be fords answer to a balast resistor? Seems using a balast resistor like chevy would make replacement a lot easier.

Yes. Ford used resistor wires up the change to electronic ignition. On the '64 Galaxie, its pink (as are most others I've seen on Fords). It reduces voltage from 12v to 7v.

Yes- - - -Ford used a resistor wire. GM switched to the same approach sometime in the early 1970s, I believe. The wire from the ignition switch to the coil primary is about 10 feet long, and doubles back on itself inside the wire harness. It has a silvery-looking conductor, and it's wrapped in fiberglass insulation.
Jerry

Pontiac did the same in the late 60s.

It also shows as a pink wire on my diagram.
So they used the wires length to drop the current. Or is there somthing else special about the wire?
I gues at the time 10ft of wire was cheeper than a balast resistor and also probably saved some time on the assembly line. I figuer its miniscule savings on a car by car basis but probably adds up prety good over a years worth of production. Good to know there are two ways of solving the amp issue during startup.

The GM resistor wire is a nickel/chrome alloy that has considerably more resistance than an equivalent length of copper. Heat-resistant insulation is necessary to prevent damage to other wires in the bundle due to the higher temperature a resistance wire creates. Ford used a bypass terminal built into the magnetic starter switch on the inner fender near the battery on some models, beginning in the 1960s.
Jerry