I have no wiring diagram to help you through this, but I am pretty sure all Buicks ? were negative to earth. Obviously if the two thick battery cables are colour coded then the red one is positive and the black negative. Have a close look at the top of the battery and see if there is a + or - stamped into it. + is positive - is negative.
Also look and follow which one of the cables goes from the battery to the engine block or body frame. That should be the negative. If you have a voltage meter it will show you which battery terminal is what if it's not stamped.
What is happening with the generator is that it's acting like a motor. Generators can do that. They can either make power ( generator ) or produce energy ( motor) depending how there're wired up. Sounds like your generator problem is related to the glitch in the circuit somewhere.
Oh, and by the way , double check that you have good clean metal to metal contact between the earth wire and the frame.
No rust or paint between the contacts.
As for the numbers on the relay , can't help you on that one. May be someone who has a wiring diagram can help here.
My guess is that 2 wires feed the coil and the other 2 feed the solenoid.
Keep plugging away.
Ken ( aka Rooster --- looking for ' 54 Buick )
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Ken ( aka Rooster --- from Down Under )
1929 Tourer model 25
1954 Roadmaster Riviera model 76R ( Irene)