Hey all, I'll try and outline my problem and see if anyone has suggestions. I have done some work on this truck, but not a ton. I've had it for about a year. I have a 1980 W150 with the 318. It's a manual if that makes a difference to anybody.

I was driving today and things seemed normal. I had just over 1/4 tank of gas. I ran out of power coming though an intersection. It felt like I had run out of gas. I was able to get into a parking lot and I did a few diagnostics. I took off the air filter and and poured a little sea foam into the carb. The motor then fires up for a few revolutions and dies off. I think I am getting good spark.
Next, I popped the fuel line off just before the original fuel filter right by the carb. When I cranked the motor no fuel came out of the line. I know there was gas in the tank, but I added another ~2 gallons to be sure. Still nothing. So I pulled the fuel pump and replaced it with a new one. I still get no fuel out of the line when I crank the starter.
The gas gauge was working fine, but now it appears not to be working. The front gas tank plumbing was cut out by a previous owner, and I haven't gotten around to replacing it.
Could this be a fuel sending unit? Is it possible to test this somehow without pulling the tank.
All replies appreciated! Thanks

 

So, the truck ran fine, when I connected the fuel line to an external gas tank. Next, I tried putting a little compressed air into the line and used soap water to look for a leak. I couldn't find one anywhere. The truck still didn't start. At some point during this I also noticed the blinkers weren't working right. I pulled a blown fuse and replaced it with a new one. The blinkers worked, and so did the gas gauge. I tried the truck, it cranked a few times and then fired up. I'm not sure how the fuse could have been the problem. Maybe it is related to the switch that changes gas tanks. Regardless it works now.