Pendragon, can you supply more details or a photograph? WM didn't make that
charger, and it may be possible to ID it as the same as another brand for which a manual is available.
For example, it might be this Promariner:
https://www.promariner.com/en/~/medi...1173-49934.pdf
But then, the manual doesn't give you much in the way of troubleshooting that you have not already checked. At order of magnitude $200 for 20 amp chargers, it may not be economical to
repair. Sad but true.