Coolant hose between the coolant pipe to driver side cylinder head. VW offered 2 parts for this hose, the 025121058C (no A/C) and then the 025121058M (w/A/C). Since the A/C hose fits either way, it's always the better choice between the two.
#2 on attached schematic.
Suitable for 1986-91 Vanagon 2WD and Syncro
Volkswagen Part Number 025121058C 025121058M