What This Housing Is and Where It Goes
The 2029177-4: It's a single-row, panel-mount housing with a locking ramp that clicks home and stays put — the ramp holds the mated pair together under vibration better than a friction-only latch. The contacts are not included in this housing — you order the male pin crimp terminals separately and stuff them in after crimping.
Mating Half and Terminal Reality
This plug housing mates with a VAL-U-LOK receptacle header of the same 4.20mm pitch and 4-circuit count — the locking ramp on the plug engages the matching ramp on the receptacle side. The male pin contacts are crimp-terminated to the wire, then inserted into the housing cavities. Because the contacts are not included, the BOM needs a separate line for the terminals (TE part number for the pin contact, typically the 1-1703532 series or equivalent in the VAL-U-LOK family). The housing accepts the standard VAL-U-LOK crimp terminal, which handles 20-16 AWG stranded wire in the standard current range for the series. No secondary TPA retainer on this single-row version — the primary latch in the housing cavity holds the terminal.