hi boo. your 78 gl is a little different than the newer wings as you have a stator, a voltage regulator and a rectifier to deal with. start by disconnecting the stator wires [the three yellow ones] an test for AC voltage at each wire.do each wire separately. give the engine a little rev an observe the AC volts. a good stator will produce around 45 AC volts. If good reconnect yellow wires an move to rectifier. The rectifier has 3 diodes the will show ohms going in only one direction. if it ohms 2 ways it is bad. let us know, frank