What is ''normal'' DD 71 series oil pressure?

With two wires on the alarm switch, one of those wires may go to the water temp alarm switch like on a generator.
Your alarm system may not be as fancy as it's larger cousins systems.

The high pressure hose is from your engine block. Probably T'd in with the oil line to your turbo.
This allows the sender assembly to be mounted where it is, or with more hose length, where ever you want.

That dd engine filter for fuel? That would be your secondary fuel filter, the Racor is your primary fuel filter.
If that dd filter for oil,,, huuummm.

Why water temp alarm? Wouldn't that come from the water temp sender?
Or is it really an oil temp alarm then ?[/QUOTE]
We got the oil senders , do you have two more for the water or one?
Like your oil sender assembly, the water temp may offer a high temp alarm that would go off around 210 - 225 *f, then a water temp sender to a temp gauge.

Your alarm senders may be daisy chained to a single bell or buzzer just to get your attention, then look at your gauges to find the error.

O K, assuming no arm switch around your secondary fuel filter, The low oil pressure alarm should come on when you turn the engine on to run, not starting or running, just on.
When you start and it's running, the switch opens and the alarm should stop.

It is oil flow that is important. PSI is the easy and cheap way to show something is there to flow.
At 28 Gallons a minute, itsa flowing and itsa flying well.

Lets look at what is getting oiled.
Monster rod and crank shaft bearings. The rod bearings are 2x larger than the largest production gas engine on the road today. The bearing surface areas is quite large.
2 cam shafts with PTO support on each end. Lots more big-wide bearings.
Blower, each end floods in oil.
Turbo, Has to move a river of oil to keep that center bushing/bearing floating and happy.

But wait, there's more; All of the shafts are gear driven. The blower is gear driven. The blower drives the gear driven fuel pump. Somewhere in there is a gear driven coolant pump. Got to keep those gears happy.
And we still send some oil up to the roller lifters for the valves and injectors.
There is a lot of heat transfer with that oil flow also.

These little 4 lunged monsters can make half the HP that my 12Vs make.
I'm scared there not moving enough oil.

You ask about dry sump.

I'm going to tell you a secret. You tell anybody I'll have to beat you with a stale noodle.
I used to build gas engines in my youth,, yes,, I am a diesel convert,, now you promised not to tell anybody...

I did learn about oil sumps and never fell in luv with a dry sump.
We just built larger oil pans. Baffles and trap doors.
I can still remember the Melling oil pump part number; M77-HV.
We modified our own pick up tube pending the sump design.
Over sized oil filter(s) NAPA 1794.

In a dry sump and belt driven oil pump or stock gear driven oil pump, pumps eats HP.
When their building up pressure and fighting against the engine to pump more up stairs, HP is wasted.
Who wants a pressure relief valve to pop, we want oil upstairs.

We built loose engines.
Now, lots of oil flying every where, lubing, cleaning, cooling and not taxing the oil pump.
We had some oil pressure at idle but your not racing at idle.

Yes, it sux when your engine blows up, but our failures were not lube issues.

Old Detroits splash oil every where, and don't need a lot of oil pressure at idle either.
I can relate and understood quickly without having to learn all over again when I converted.

In your picture, looks like somebody had already replaced the gauge sender, probably the wrong one.
Now, Go fishing and get those puppies hot and report hot oil pressure at idle.

I forgot that. Then grab da family and go for a ride.