I have having problems with my 1969 Chevelle. Sometimes when I try to start it it will do nothing but if you put the battery charger on it it will fire right up. This is what I have replaced and it still does it: battery, starter, added ground wires, alternator. It does not do it all the time but it is aggravating because I do not know when it will happen. Any help would be greatly appreciated.

Maybe a bad ground to the engine block. Take if off and clean real good. How is the reagulator?

regulator is fine.

Is the battery dead when it won't start? You need to determine that for sure. If the battery is dead then you have a drain some where that is killing it. If it's not dead then you have a bad connection or corroded wires. Battery cables will corrode inside the cover. Any movement of the cable may temporarily restore the connection.

This post should be in the electrical forum.

You need to do some voltage drop tests to verify you dont have a resistance in your system. When this occours, use a multi meter and turn the dial to the 2 volt DC setting. Place one lead on the center of the battery post, and place the other on the battery cable clamp. While in those positions have a helper attempt to start the motor. You should not have a reading higher than 1.5 volts, if you do you have a resistance at that spot. clean the cable and terminal.

Then while keeping the center of the battery post connected, connect the other to the other end of the battery wire, and do the test again, and then again to the bolt that the cable is connected. You also want to take an actual battery reading before, during and after the attempt at starting. Get the starter tested while on the car, you can take the car to an auto parts store, and most have on the car testers.

Also check the voltage and connections of the solenoid wires.