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The clever simplicity of our ignition switches
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56D500boy
Posted 2022-04-10 3:20 PM (#620818)
Subject: The clever simplicity of our ignition switches



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I recently "refound" my Brooklands 1949-1959 Dodge Road Test book and decided that I should read it cover to cover. This AM, I started with the 1949 Dodge info. There on page 6 was a diagram that I seen before had probably forgotten about: How the triple contact, spring loaded ignition/starter switch worked. As I looked at the diagram, I thought that whoever came up with the design, with three moveable contacts and four variable but fixed contacts of variable width, hopefully got at least "Employee of the Month" (and a nice patent).

As seen in the diagram below, from the Brookland book, when the key is turned to the left, power is directed to the Ammeter and only the Accessory contact. The third moveable contact does NOT make contact with any fixed contact.

When the key is turned fully to the right, i.e. START, power is directed to the Ignition, the starter and the Ammeter; the fixed accessory contact is not contacted at all, i.e. any accessories, like the radio, the heater fan, etc. are powered off (to decrease the load on the battery and direct more power to the starter).

When the key is released after START, the three moveable contacts contact the ignition, the ammeter and the accessories. Only the starter contact is by-passed (which obviously makes sense).

I think the 1949 diagram assumes that the power from the battery comes into the switch in the middle and is then fed out to the three moveable contacts and then two or three of the four fixed contacts, as appropriate.

By 1955/56 the design of the ignition switch was a bit different, with the power from the battery coming into one of the side terminals of the "new" ignition switch, as shown below. However, the same type of power distribution happens as the 1949 switch:

Accessory = Ammeter and Accessory terminals
RUN = Ammeter, Ignition and Accessory terminals
START = Ammeter, Ignition and Starter terminals (no Accessory terminal)

For me the function of the ignition switch and the Ignition and Accessory terminals was important when I "improved" my eBrake light (converted it to LED, following Dels56's lead). In stock form, the eBrake warning light the warning light was connected to the ACC terminal and therefore was on when the brake was on, both with the key turned to RUN (IGN) and Accessory (ACC). Since I didn't want the warning light on while parking and listening to the radio (converted to AM/FM/Bluetooth/USB/iPod) with the key turned to ACC, while I was working on the car, I changed the source of the power to the warning light to the IGN terminal on the back of the ignition switch. Therefore the warning light is only on when I turn the key to RUN.

I am sure all this "information" is old news to most of you but it might not be to some of you. As usual (for me), once I figure something out, I like to share what I have learned. Sorry about that.



Edited by 56D500boy 2022-04-10 4:43 PM




(IgnitionSwitchFunctionFrom1949DodgeInfo_Annotated.jpg)



(MoparIgnitionSwitch_3.jpg)



(MoparIgnitionSwitch_4.jpg)



(MoparIgnitionSwitch_5_Annotated.jpg)



(FourPoleIgnitionSwitchConnections.jpg)



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Attachments IgnitionSwitchFunctionFrom1949DodgeInfo_Annotated.jpg (197KB - 41 downloads)
Attachments MoparIgnitionSwitch_3.jpg (119KB - 38 downloads)
Attachments MoparIgnitionSwitch_4.jpg (131KB - 41 downloads)
Attachments MoparIgnitionSwitch_5_Annotated.jpg (193KB - 38 downloads)
Attachments FourPoleIgnitionSwitchConnections.jpg (36KB - 40 downloads)
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57burb
Posted 2022-04-10 7:48 PM (#620826 - in reply to #620818)
Subject: RE: The clever simplicity of our ignition switches



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Many of those early electromechanical devices were very clever.

Small note, that may be relevant for some of us here. FL cars built with the "Start" button on the pushbutton shifter have ignition switches that omit the center "Start" terminal as shown below. It's the same basic switch, just missing that one terminal.

I found it funny that the assembly line maintained a supply of two switches instead of just one switch that would work in every car.



(MoparIgnitionSwitch_5_Annotated.jpg)



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Attachments MoparIgnitionSwitch_5_Annotated.jpg (193KB - 39 downloads)
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56D500boy
Posted 2022-04-10 9:33 PM (#620830 - in reply to #620826)
Subject: RE: The clever simplicity of our ignition switches



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57burb - 2022-04-10 4:48 PM
Many of those early electromechanical devices were very clever.
Small note, that may be relevant for some of us here. FL cars built with the "Start" button on the pushbutton shifter have ignition switches that omit the center "Start" terminal as shown below. It's the same basic switch, just missing that one terminal. I found it funny that the assembly line maintained a supply of two switches instead of just one switch that would work in every car.


I did not know that but I just searched and the switch of which you speak is PN 1770 040 and, yes, it has no center terminal. They could have dealt with that with keeping the center terminal and adding a screw on (10-24) dummy cap to prevent things being connected to the temporary on (starter) terminal. Oh well....

This:





(1770040IgnitionSwitchForNeutralStartingSystems_1.jpg)



(1770040IgnitionSwitchForNeutralStartingSystems_2.jpg)



(1770040IgnitionSwitchForNeutralStartingSystems_3.jpg)



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Attachments 1770040IgnitionSwitchForNeutralStartingSystems_1.jpg (110KB - 37 downloads)
Attachments 1770040IgnitionSwitchForNeutralStartingSystems_2.jpg (37KB - 39 downloads)
Attachments 1770040IgnitionSwitchForNeutralStartingSystems_3.jpg (41KB - 37 downloads)
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LD3 Greg
Posted 2022-04-11 12:14 AM (#620837 - in reply to #620830)
Subject: RE: The clever simplicity of our ignition switches


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Yes. The difference between push button start and key start! Not only different switches but different wiring harnesses. WHY?? One standard on a Coronet and the other standard on a CR!!

Wait till 59-60 when you had I1and I2 (ign 1 and ign 2) terminals on the ignition switch where ign 1 sent ballast resister power to the coil and ign 2 sent battery power to the coil. Ign 2 was always a momentary spring loaded contact only for maximum starting voltage.

The most clever switch was the late 50s turn signal switch. Before you disassemble one be sure you have a decent back up, you know, you will need it after all those little springs go all over the room!!

Greg
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57chizler
Posted 2022-04-11 12:55 PM (#620845 - in reply to #620818)
Subject: RE: The clever simplicity of our ignition switches



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Simplicity is convenient but, when you try to run a lot of accessories, the small contact area can be overloaded. That's why most modern switches have multiple IGN and ACC terminals...spreads the loa
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LD3 Greg
Posted 2022-04-12 12:53 AM (#620849 - in reply to #620845)
Subject: RE: The clever simplicity of our ignition switches


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57chizler - 2022-04-11 12:55 PM

Simplicity is convenient but, when you try to run a lot of accessories, the small contact area can be overloaded. That's why most modern switches have multiple IGN and ACC terminals...spreads the loa


While “you or I or we” might add accessories to the “acc.” circuit, the factory never did that!
The headlight switch and wiper switch got battery power protected by separate circuit breakers. Even the back up light circuit, which was prone to shorts due to careless loaded trunk items got power from a circuit breaker, not accessory switch power. Added factory options like A/C and auto pilot also got battery power with inline fuses. The kick panel circuit breakers provided battery power for electric windows, seat, convertible top and power antenna. The radios in our cars had factory in-line fuses.

When our cars were new the factory had already spread the electrical load!! Engineering excellence in my opinion!

Greg.

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57chizler
Posted 2022-04-12 2:30 PM (#620855 - in reply to #620849)
Subject: RE: The clever simplicity of our ignition switches



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You misunderstand, I never said the circuits aren't well protected....circuit protection and contact load are different things.
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