Hi,
Don’t know the answer but here’s a link to the [https://drive.google.com/open?id=14fY2LKngC7JT4WN6Ct039gdKCrJaCr9T|VW Transporter T4 1982-1992 Service Repair Manual] that may provide the answer.
I haven’t looked at it as it is a 113Mb .pdf file download so hopefully it will have what you want.
The download link was copied from [https://carmanualsclub.com/volkswagen-transporter-service-repair-manuals/|here]