Abstract: In this work, upward negative precursors at the triggering wire tip during the ascent of the rocket were explored using comprehensive data from the rocket-triggered lightning experiment. Except for those typical precursors with a peak current of tens of amperes, abundant weak current pulses were identified, which is attributed to the high vertical resolution current detection. All isolated current pulses were weak, and those typical-intensity precursors (or clustered precursors) were preceded by weak current pulses at an interval of approximately 20 μs. For the weak, impulsive, and ripple pulses, their geometric mean values for peak current were 3.6, 32.2, and 11.1 A; moreover, rise times for these pulses to increase their current from 10% to 90% peak were 0.39, 0.9, and 3.2 μs, durations were 2.8, 5.1, and 12.7 μs, and charge transfer values were 4.7, 50.8, and 83.2 μC, respectively. The typical-intensity precursors formed visible discharge channels that can be detected using optical means, and the channel development of those clustered precursors involved stepwise features, consistent with the initial sustained upward leaders, with an average 2D speed in the order of 10⁵ m/s. The temporal and spatial relationships of adjacent precursor-producing channels were also examined. The new precursor channel was found to start at the height of the previous channel tip. The important adjustment of charge distribution due to the stepped channel extension reduced the electric field intensity in the channel region. The precursors were actually un-sustained leader development, producing an initial leader channel segment at the triggering wire tip, but they eventually extinguished due to insufficient conditions.