I tried to change the fuel filters in my 2020 Ran 3500 and now have a terrible fuel leak that seems to be behind or to the rear side of the filter housing like some how a line got loose. What have I done?

 

I would take the top off the filter housing and check it and the housing for cracks (in case you over tightened). It may be easier to see if you take a few closeup photos with a flashlight giving light at a different angle.

Did you put the new O-ring on after you took the old one off?

Was the top tightened enough?

Back to morning brew . . .