speedometer question& ignition question

Hi, Im new to the site, i have a 70 dart swinger with a slant 6. I have two questions, the first is i took the speedometer cable out back behind the dash, then when i went to plug it back in the bottom tab on the cable where it snaps into the speedometer broke off, so now when i try to plug it back in, it wont stay in. since the tab is broke, does that mean i have to buy a new cable?

I'm thinking you'll need a new cable housing - ought to be easy to find.

also lately i have noticed when i start the car the only way the engine will stay running is when i keep pressure on the key, but as soon as i let go the engine dies. is this a bad ignition switch or something else? any help would be appreciated thank you

Sounds like you have a bad ballast resistor.