The LORD therefore be judge, and judge between me and thee, and see, and plead my cause, and deliver me out of thine hand. And it came to pass, when David had made an end of speaking these words unto Saul, that Saul said, Is this thy voice, my son David? And Saul lifted up his voice, and wept. 1 Samuel 24:15-16
Plead in the KJV does not mean to pray, supplicate, beg, or implore. It always has the sense of seeking a judgment, and means to argue for or against a cause, to urge the claim or state the case of a person. This KJV usage survives in legal terminology. "If ye plead against me my reproach" means "If you make my humiliation an argument against me" (Job 19:5). "There is none to plead thy cause" means "There is none to uphold your cause" (Jeremiah 30:13). "Plead for a man with God"—the verb here is the one which is translated "reason" in Job 13:3, "I desire to reason with God," and in Isaiah 1:18, "Come now, and let us reason together."
The word "plead" does not appear in the New Testament. The four Hebrew verbs which "plead" represents in the KJV have as their basic meanings contend, prove, judge, govern; and each may imply action as well as words. Proverbs 31:9 reads, "maintain the rights of the poor and needy." Isaiah 66:16 has "execute judgment"; Jeremiah 2:35, "bring to judgment"; Jeremiah 25:31 and Ezekiel 17:20; 20:35, 36; 38:22, "enter into judgment."
(The Bible Word Book, Bridges & Weigle, pg 261)