Does anyone have any thoughts why the engine will fun for 15 minutes then stalls. Boost it, runs then stalls?

 

Check the voltage at the battery terminals both before you start it and while running. The running voltage should be between 13.6 and 14.2 volts. If it's not either your alternator is bad or the wiring is faulty somewhere. If this is the case check to make sure you have continuity between the battery + and the charging post on the alternator.

 

thanks for the answers guys, it gives me some good starting points. I checked the voltage and it is running at 11.6 at the alt and the battery.

 

Then the regulator is dust. It sounds to me like the battery is draining and the car dies. If you have a real 442 then it's internally regulated and you'll need to replace the alternator. Take it in and have it tested to be sure. Also double check the wiring to make sure it's in good shape.

 

I just received all the new wiring so I have some work to do. I think it is the alt because when I check right at the alt it is reading 11.6 to 11.8. I checked the regulator and its showing the same thing and the battery is showing the same even after I disconnect the battery. Do you think I should install a stronger alt?

 

Wait a min.....you have an external regualtor? If that's the case it's a re-badged Cutlass or F85. All 442s in 1970 were internally regulated.
That said it could be the regulator that is bad. And unless you have a crazy stereo in it I wouldn't worry about upgrading the alternator. If you do then you should ditch the externally regulated one for an internally regulated one.

What harness did you get?