Engine smooths out when positive cable removed

[gysgtc]

Trying to help my brother out with his engine problem. He has a mild cam in it. When it is at idle it lopes like it has a cam in it but if you pull of the positive battery cable it smooths right out. Discovered this because when you turn the headlights on the engine dies. Trying to figure out what is going on. He replaced the points in the distributor with a module when he rebuilt the engine so no points anymore. Any suggestions? Thanks