1994 chevy truck the connection from the battery to the starter had broken so I bought a replacement end at Napa. Now when I turn the lights on, apply the brakes or turning signals the truck stalls. The truck won't start until I turn the lights off. What could be wrong

Remove and fully charge the battery. Most auto parts stores will test and charge batteries for free. My bet is that the battery is bad.

1994 chevy truck the connection from the battery to the starter had broken so I bought a replacement end at Napa

Which actual end did you replace?
If your truck had the little pig-tail wire along with the larger red cable, make certain that got back in.
Both ends of both cables need to be clean and secure.

Which actual end did you replace?
If your truck had the little pig-tail wire along with the larger red cable, make certain that got back in.
Both ends of both cables need to be clean and secure.

I replaced the end at the starter. I had the battery tested and was good. I had pull started the truck and drove it 4 miles and everything worked okay. Found the broken end and Napa gave me a compression type end. I cut the insulation back and installed as per direction. The connection is for a 6 gauge wire. The cable is a factory cable and I don't know what the gauge wire is. Could that cause the issue also?

6 gauge sounds kinda small but if all of the original wire bundle fits in it, that's the proper size.
Getting back to "when I turn the lights on, apply the brakes or turning signals the truck stalls," you may have another issue. Your alternator may not be working properly and/or you may have something in the lighting system that is shorted and causing excessive draw, which can overload and stall the engine.

This will likely require hands-on diagnosis and inspection. Who does your other work on your vehicle? Can they diagnose this electrical problem for you?

Thanks for all the help... Found the ground wire from the frame to the body was broken. Repalced it and all is well.

6 gauge sounds kinda small but if all of the original wire bundle fits in it, that's the proper size.
Getting back to "when I turn the lights on, apply the brakes or turning signals the truck stalls," you may have another issue. Your alternator may not be working properly and/or you may have something in the lighting system that is shorted and causing excessive draw, which can overload and stall the engine.

This will likely require hands-on diagnosis and inspection. Who does your other work on your vehicle? Can they diagnose this electrical problem for you?

Thanks for the help! I found the ground wire from the frame to the body was broken. Replaced it with 10 gauge and all is well!