Plasticard, zip ties, diamond pattern plasticard. Random tubes and old wires from old devices. Gubbins from kits, tanks especially are good for extra mechanical looking bits.
Primed black, then painted with AK Dark Rust, not silver or grey. This keeps them looking old and rusted.
Using plastic zip ties to create your cyber-punk base is so coo, I've never seen that done before!
@tomistomming some pics of previous industrial bases here. Hope these help.