Car will not stay running without holding the key down

[Afacente]

71 challenger will not stay running when i let off the key. Put in a new ingntion switch and is still happening i can start it then turn the key back fair enough for the starter to disengage but still have pressure on the key and it will stay running as soon as i take the pressure of the key it instantly dies any help would be greatly appreciated.

[Ed]

Do You have the resistor on firewall ?  white square resistor    thats whats wrong.

[Ed]

you bypass that resistor while starting to get hotter spark.   you can jumper those wires together to prove thats whats wrong.   when You put new resistor in it may smell the first time  they gey hot thats why they are ceramic.

[fc7cuda]

Could be ignition switch.

[anlauto]

Sounds like a ballast resistor 

[Chryco Psycho]

put a test light into the blue wire at the ballast & see if you have power at the ballast int he run position , if you do it should be the ballast if not it will be the ign switch or connection at the bulkhead or column

[Afacente]

The ballast resistor has been removed on this car the wires for it are not connected to anything it has a msd street fire ingntion box and speed master distributor if that helps also it stared and and was running great before then the next day this problem happened

[Brads70]

The ballast resistor has been removed on this car the wires for it are not connected to anything it has a msd street fire ingntion box and speed master distributor if that helps also it stared and and was running great before then the next day this problem happened

electrical is not my strong point but if I remember right you need to joint the 2 wires from the ballast resistor( brown and blue?) to the small red wire? I used a 6al box and remember having to do that I think....It came with a plug and play wire to do that. 
https://www.jegs.com/InstallationInstructions/100/121/121-5520.pdf

[Chryco Psycho]

exactly the ign needs power in start & run position so the blue & brown need to be connected together

[Afacente]

Thanks for the response got it fired up today ended combing the 2 wires then spliced it in to the red wire and it fired right up

[Chryco Psycho]

Congrats , it is an easy mistake to make