This movie had a lot of thought put into it and it shows. Love or hate Banno's directorial style, the film's pacing and attention to detail are very deliberate. Godzilla vs. Hedorah
has been one of my favorites since the first time I saw it and even after all these years, I'm still noticing new things when I rewatch it. Today I just realized that Godzilla doesn't willfully activate the electrodes to fry Hedorah the first time he blasts them. Godzilla learns his atomic breath can do that by accident when he means to blast Hedorah.
At the outset of their battle at Mt. Fuji, Hedorah hits Godzilla with several acidic sludge splats, including one on Godzilla's face which leaves his left eye swollen shut for the remainder of the film.
After lasering Godzilla and leaving him writhing on the ground, Hedorah targets the people. Godzilla gets Hedorah's attention again with a blast of atomic breath. Uncharacteristic of Godzilla, his atomic breath misses his target a little to the right, because now he's aiming with just his right eye.
When the military is able to lure Hedorah with flashing headlights, they get him to walk between the electrodes but they don't yet have the power to activate them. Godzilla once again reinstigates his fight with Hedorah using his atomic breath, again missing Hedorah by aiming too far to the right. This inadvertently activates the electrodes.
But Godzilla wouldn't have known at first what those electrodes would do. He couldn't know that the humans were struggling to activate them or that his atomic breath would inexplicably do the trick. Once he saw the result he kept doing it but when he activated the electrodes that first time, I think Godzilla did it completely by accident due to Hedorah burning his left eye and throwing off his aim.