Getting fresh water system working

Found a few threads about the fresh water system but still have a few questions. On my new to me 1990 48 Californian MY I spent a night on the boat with some water issues. The water gauge shows full but no water. The water pump runs continuously. A strainer right before the water pump never had any water in it. So I put some water in the system via a hose with the water inlet on the side of the boat. Probably 25 gallons or so. Never got anything working. So,
Question 1 - Work on the idea the water gauge probably doesn't work, so if I put water in the systems is there an overflow hose that I should find somewhere? Question 2 - Would the system need primed?, fill the strainer and open a faucet? Question 3 - I'm guessing but the water pump is probably at the same level as the middle of the tank, so no priming required?

The Brockerts

I would fill the tank until water flows out the vent. Then you know that’s not the problem. You didn’t mention what model pump you have but it shouldn’t need priming. Open a faucet and let it run awhile, if no water flows, it may need a kit.

Once the tank is confirmed full, check for any valves, etc. in the system that might be preventing water from getting to the pump.