This wiring kit has everything you need to hook up 2 compressors. This is what we use on our show quality installations.

Includes:
(20-ft) 4-Gauge, Tinned 100% Oxygen-Free Copper (1,666 strands), Flexible Red Power Cable
(10-ft) 8-Gauge, Tinned 100% Oxygen-Free Copper, Flexible Red Power Cable
(1 pc) 4-Gauge Mini-ANL Fuse Holder (main fuse holder)
(1 pc) 70-amp Mini-ANL Fuse (for main fuse holder)
(3 pcs) Standard/Mini/Micro Fuse Taps
(3 pcs) Standard/Mini/Micro 5-amp Fuses
(1 pc) Small Hex Wrench Tool
(1 pc) Large Hex Wrench Tool
(6 pcs) Screws For Fuse Holder Mounting
(2 pcs) 14/16-Gauge Blue Female Connectors (for pressure switch)
(1 pc) +12-v/100-amp EVOLVE Heavy Duty Relay
(2 pcs) 4-Gauge Ring Terminals (Pre-crimped)
(2 pcs) 8-Gauge Ring Terminals (Pre-crimped)
(2 pcs) 8-Gauge Mini-ANL Fuse Holder (for compressors)
(2 pcs) 40-amp Mini-ANL Fuses (for compressors)
(20-ft) 18-Gauge Yellow Wire w/Ring Terminal
(5-ft) 18-Gauge Black Wire w/Ring Terminals For Relay / Pressure Switch
(25 pcs) Black Cable Ties
(2 pcs) 12-Gauge Ring Terminals (for compressors grounds)
(2 pcs) 6mm Nut/Bolt/Washer Assemblies (for compressor grounds)
(2 pcs) 6mm Nut/Bolt/Washer Assemblies (for mounting relay)
(1 pc) 6mm Nut/Bolt/Washer Assemblies (for pressure switch ground) 
Wiring schematic is online to download.