75 Series Dash Lights/Alternator issue

[Drift Technician]

Got a 2H turbo diesel in a 75 series ute, no known electrical problems except dual battery setup has never worked.

Went 4wding the other day/night got back, used local fire hose to wash down engine bay.

Go out in morning to take to work, no "dash" lights, ie no battery light, no filter lights and no glow plug light coming on for couple of seconds. Took a little bit to get it started then drove to work. Took a bit to start to get home, on way home it appeared was charging fine all of a sudden, get home and the lights on dash are back to normal after test.

Wash engine bay down, go to start hour later and same problem.

Have checked what fuses I can see, replaced some with no luck.

Have wiggled wiring etc with no luck either.

Fire hose was predominatly used on battery/alternator side although I dont think it is the battery as the dash lights are gone as well.

Not dash lights themselves as the glow plug one flickers on for micro second and the park brake/4wd light and dash lights of a nightime all work.

Any help would be great.