Sell short when a swing high forms after a breakout.
The following is from Elliott Wave Principal by A.J. Frost and Robert Prechter:
An ending diagonal is a special type of wave that occurs primarily in the fifth wave position at times when the preceding move has gone "too far too fast," as Elliott put it. In all cases, they are found at the termination points of larger patterns, indicating exhaustion of the larger movement. Ending diagonals take a wedge shape with two converging lines.
Each subwave, subdivides into a "three" which is otherwise a corrective wave phenomenon producing an overall count of 3-3-3-3-3. The fifth wave of a diagonal triangle often ends in a "throw-over," i.e. a brief break of the trendline connecting the end points of waves one and three. While volume tends to diminish as a diagonal triangle of a small degree progresses, the pattern always ends with a spike of relatively high volume when a throw-over occurs.
An ending diagonal is a special type of wave that occurs primarily in the fifth wave position at times when the preceding move has gone "too far too fast," as Elliott put it. In all cases, they are found at the termination points of larger patterns, indicating exhaustion of the larger movement. Ending diagonals take a wedge shape with two converging lines.
Each subwave, subdivides into a "three" which is otherwise a corrective wave phenomenon producing an overall count of 3-3-3-3-3. The fifth wave of a diagonal triangle often ends in a "throw-over," i.e. a brief break of the trendline connecting the end points of waves one and three. While volume tends to diminish as a diagonal triangle of a small degree progresses, the pattern always ends with a spike of relatively high volume when a throw-over occurs.