Battery drains only when car is running... Help

i have a 63 Valiant with the /6.

When the car is running, the battery just drains out til its dead!

The battery is good, just had it tested. it holds a charge when the car is OFF, with key in any position.

The alternator is good as well, it will keep the car alive but won't charge the battery.

I've checked for loose connections and found none, there are no exposed live wires to arc out on either.

I'm pounding my head against the wall here guys..

Any ideas?