Fuel inlet line and return line switched on the fuel sending unit 1988 Comanche 4.0

[Comanche man Don]

Hi guys. After installing new rubber fuel lines coming off my sending unit the truck doesn’t want to start and if it does it runs rough before dying. I’m wondering if I didn’t get those hoses mix up.meaning my pump is pushing gas through the system backward through the fuel regulators and rail. Anybody ever had this issue? Or know what the symptoms of that would be. ? Also there is what appears to be a vacuum line coming off the back of the regulator. When I pulled the rubber boot of the vacuum (unplugging it from the fuel pressure regulator) I noticed it was filled with gas. Is that a vacuum line or is it suppose to have gas in it.?thanks.

[Ωhm]

2 hours ago, Comanche man Don said:

Is that a vacuum line or is it suppose to have gas in it.?

Vacuum line. If you got gas in it, faulty Fuel Pressure Regulator.