When the engine is turned on the electrical system acts like it is being nearly completely drained. Lights, etc are very dim and engine stalls sometimes. Also can only be started by jumping with another car. However, when engine is off, battery has nearly full charge and lights, etc come on bright. Any idea what the problem might be? Alternator is fairly new and I checked the fuses.

It sounds like it could be a short. The system doesn't need much power to run everything with the motor off. There could be a bad ground strap?

Just a thought.

Sounds like it is a problem with wiring that is only energized when the ignition is turned on. Does the problem exist when the ignition is on but the motor is not running? Visually check your wiring where it passes through the firewall & everywhere else that it may rub on something for shorts. Look to see if there is melted insulation on any of your wires, either from being to close to something or from heating up due to too much current. If the problem exists when the motor is off but the ignition on maybe try turning on the ignition while the engine is cold and feeling the wires for a warn one. Try pulling fuses while the car is running. If there is a short in one of the circuits things should go back to normal when the fuse is pulled. Good luck. Electrical problems suck!

Steve