What does the warning light with a arrow going through rectanle 8 dots mean in 2004 Ford F250 Turbo Diesel?

That sounds like the low engine coolant level warning light. The rectangle with eight dots is a common symbol representing a coolant reservoir or radiator. The arrow through it usually signifies a low level or problem within the cooling system.

In a 2004 Ford F250 Turbo Diesel, a low coolant level is a serious issue. Ignoring it can lead to catastrophic engine damage due to overheating. Immediately check your coolant level and if low, add coolant (using the correct type for your diesel engine – check your owner's manual) to the reservoir. If the level is fine, or it continues to drop, you have a leak somewhere in the system and need professional help to diagnose and repair it. Driving the truck with low coolant is very risky.