OK, you should have.......

3 Gauges.

1 Control Unit

1 Sensor of some kind for each Gauge. The Black item in the last pic is the Boost sensor. I think you are missing the other 2 unless there are other items that you havent photographed.

1 Wire for each Sensor with a large plug on one end and a Small Plug on the other. I think these are what are in the top 2 pics. The small plug on the end of each cable will only fit into its correct port on the Control Unit.

1 Link Cable, probably about 2ft Long? (small White plug on each end). This goes from the Control Unit to the First Gauge.

2 Short'ish Link Cables (with small White Plug on each end). These link the subsequent gauges.

1 Power Harness. This has a Small white plug on one end and 4 Wires, which are the Electrical Supply connections for the system.

Yes, I can supply any bits that you need. Just show me exactly what bits you already have and I will fill in the blanks. Email them if you want.

HTH.