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Ignition Switch No Start

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I have had quite a tough time with my '51 Meadowbrook over this past year. The latest of issues started with a faulty ignition switch; it would shut off if you hit a bump and would have to jiggle the key to get it to gain continuity again. It's a strange one that has three terminals, listed as ST, ACC, AM, and a central wire that is fixed to it under a metal sheathing that goes through the firewall and attaches to the horn relay.  The switch I bought was from a '50 Coronet and has four terminals, listed ST, ACC, IGN, BATT.  I'm not sure what the AM standards for but it had one wire attached to it. The ST had one wire attached to it. The ACC had the rest of the wires, such as the radio and heater motor, attached to it. So I connected the ST wire to the ST terminal of the new switch, the AM wire the ACC terminal, the set of wires from the ACC in the old switch to the IGN terminal in the new switch, and I ran a wire from the BATT terminal to the outside of the firewall to the horn relay. I did this based on position of the wires on the switch. Well that didn't work as it shot my Ammeter down to -50. So I found that the wire that is attached to the ACC wire had current in it and connected it to the BATT terminal. From there that left the wire on the ST, the wire on the BATT, the wire going to the horn relay on the ACC, and the set of wires on the IGN.  I turned the key and the starter turned and turned but would not fire up. I found that the only way it will fire up, and it fires up immediately, is if I turn the key to ON and connect a wire from the IGN to the ST. I can't understand why it will not fire is I turn the to the START position. I also found out that if the engine is running and I turn the key from ON to ACC the engine continues to run. What am I messing up, or is this switch faulty as well? And through my playing with this switch I fried the LED flasher relay so I need to replace it.

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Try to find a wiring diagram, or do some serious tracing. The reason it won't start is likely that you have the wire to the coil connected to the acc side, which disconnects when you move the key to start position.    Key on should energize both the acc and the ign connections, but only ign is energized in start position so that the voltage fluctuations don't get into the radio or other sensitive accessories.  ( Why engine runs on acc). The wire from the horn relay is likely your main power. (Batt)  Acc position lets you run radio and probably heater fan, but no power to the coil.  AM must be ign ( coil) but that's a strange one to me. 

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Simple - 

One terminal RECEIVES power from the "Battery" 

One terminal sends power to the starter motor/solenoid

One terminal sends power to the coil.

One terminal sends power to everything else that needs power only when the key is on. (accessories such as radio)


When the key is turned to "ON" power goes to the coil AND the accessories.

When the key is turned to the (spring loaded) "START" position power goes to the starter-starter solenoid. 

When the key is turned to the left (accessory position) power goes ONLY to the radio etc. No power to the coil.


So one wire on each terminal except that accessory terminal. Every accessory that you want to turn off and on with the key can be stacked up here. 


I suspect the AM terminal is "Armature". There are many places that battery power can be taken from under the hood.

The battery itself.

The armature terminal of the regulator.

The battery feed that is going to the horn relay. 

I dont know where Chrysler might have picked up their battery power from, there are probably reasons why they might have chosen to pull it from one place or another but its that same basic idea. 




Edited by m-mman (see edit history)
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  • 1 month later...

Up through 1949, and probably later in some cars, there was four ways of starting a engine. The hand crank was long obsolete, but, what the hey. Next was the floor start switch, then the dash mount push button and then the additional, spring loaded position on the ignition switch. Also, starter interlock switches was being incorporated with transmission selector positions and brake pedal depression to safeguard against accidental engagement of the starter. And then, there was individual improvisions which negated any previous knowledge acquired regarding any of the four. My suggestion is to get a volt test meter with resistance measuring ability and test each position of the switch you intend to use. If it has a spring loaded position, the terminal connected to the starter solenoid should show resistance (no power is connected) should be indicated between the pos battery terminal and the connector associated with energizing the starter solenoid. The coil should be activated in switch positions other than ACC and OFF (you don’t want the coil energized while listening to your Elvis eight track tapes). Of course, if the car has a start switch of a sort rather than the key.......get a wiring diagram for that car.........good luck.

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