What is it about Robert Johnson that invites speculation? From his (re)appearance in popular music in the 1960s, to his resurgence in the early 1990s, he must be the African-American musician about whom most drivel has been written and spoken.
Now that the biography by Bruce Conforth and Gayle Dean Wardlow is out—my review: essential reading—, speculation should diminish significantly. Never mind that, I now offer you a bit of guessing, at least to provide some context regarding Johnson and the electric guitar, an instrument with a tradition in blues and rock heavily influenced by Johnson, even though he never really played it himself.