speedometer question& ignition question

[lagwagon29]

hi, im new to the site and i have a 1970 dart swinger slant 6. I have two questions that i hope someone can help me with. I took the speedometer cable out and when i went to put it back in the tab on the bottom that clicks it in place broke off and now the cable wont hook in. Will I have to buy a new cable or is there someway to fit a new connector at the end of the cable that is already in the car. Also, another question lately I have noticed when i start the car the only way it stays running is when i keep pressure on the ignition switch. as soon as i let go of the ignition switch it dies. I dont know if its the ignition switch that is bad or what. any help would be appreicated. thank you