not getting fuel to fuel pump

There has to be a problem with the supply line either being kinked or the pick up tube in the tank isn't properly installed. Have you checked that? If you remove the supply line from the pump and blow air through it with the gas cap off, can you hear the fuel in the tank bubbling?

It will run if I put line to the pump in a gas can. No kinks. Brand new sending unit assembly. It had dual tanks but I disconnected the driver side tank and ran line straight off the tank to hard line bypassing. Switch valve. Don't know what else to try?

Okay... the vehicle is a 78. I still have my 78 chevy, so I can compare. Let me confirm. You still have a mechanical pump mounted on the passenger side of the engine, correct? If so, you ran a new fuel line from that pump to the new fuel tank, correct? If so, if there are no lines kinked or damaged, the pick up tube in the tank is low enough to reach the fuel, it should work. If that is the case and it will draw fuel from the pump to a gas can, it makes no sense that it won't from the fuel tank. Is there anything between the tank and pump like a fuel filter that could be clogged? And I hate to ask again, but you are certain that the pick up tube in the tank is low enough to reach the fuel? If you remove the fuel line from the pump and blow air into it, do you hear it in the fuel tank?

Ok. I was afraid that I did this but I thought about figured I must of put the soft lines on backwards at the sending unit. Sure enough when I reversed them it started and stayed running. I was sure they were right. Oh well live and learn. Thanks for the response. Much appreciated.

That will do it. Glad you got it fixed. Let me know if you have questions in the future. I love the old trucks.