More electricity:
Ennis refuses to apply for a job at the power company. In the story, it is only shortly mentioned. But in the movie, it is more broad.
From screenplay:
Alma reads the want ads
Alma: Ennis...they got a openin' over at the power company. Might be good pay.
Ennis: Clumsy as I am, I'd probably get electrocuted.
First, I don't think of Ennis as clumsy and doubt he sees himself like that. Probably only an excuse for not applying there and avoiding a discussion right then; in this scene he is hurriedly preparing for a trip (the one when he forgets the tackle box and Alma reminds him).
Second, on a symbolic level, Ennis doesn't want to get too near to sources of great amounts (high voltage) of electricity. But he sure likes the little sparks/electrical current snapping between him and Jack.
Just like he wants to be with Jack, but not too near, meaning not permanent. And for the same reason: he is afraid to die from it. Being electrocuted while working for the power company respectively being beaten to death for living with Jack.