Engine wiring please?

I have checked all the fuses in the fuse box and they are working fine, but I am only getting 5volts to the fuel pump at the tank. Is there another relay that I need to check? If so where is it and how do I check it? If that is not the problem what is? Swapping out the relay did not resolve the issue. When I turn the key I get 12V to the pump for a brief period, but the pump does not activate. What can I try next. I connected another battery to the pump and it starts working, could it be the connector at the pump? I charged the battery replaced the connector at the pump. Using the new splices I checked the voltage at the wires. The combination that powers the fuel pump does not get any voltage to it. All the other combinations of wires get 12v for a second or two when the key is turned on, then all go to zero v except the purple/orange combination which gets 1.27v all the time. What can I try now?

I get a 12v reading on 4 of the 6 combinations of the 4 wires. One one combination I get 1.27 volts and the other connection I get 0v. The combination that gets 0v is the one that powers the pump. I am testing these voltages at butt connectors I used when I replaced the connection to the fuel pump. So the pump never turns on when the key is turned. I connected the fuel pump to another battery and then started the truck. The truck started and ran until I disconnected the power to the pump. What can I try next

I had a same problem. It turned out to be a bad fuel pump ground connection. The ground is located on the frame back by the rear bumper driver side. The self threading bolt was stripped out.

What you are describing may not even be an actual "problem". My 1990 S10 gave me the same thing. I discovered that the system is actually designed to do that! The fuel pump relay is supposed to only energize the fuel pump for a few seconds to pressurize the fuel system so that the engine has enough fuel to start, then shut off. It then transfers control of the fuel pump to another relay. This relay is activated by an oil pressure switch. When the engine actually starts, engine oil pressure signals the second relay to again send 12V to the fuel pump for continued operation. This is a safety feature to protect the engine. If you suddenly lose oil pressure, the fuel pump is shut off, stopping the engine, to prevent burning up the engine. I figured this out after some research and studying the electrical diagrams. If the fuel pump runs fine with 12V hooked directly to it, the pump is most likely OK. A check of the fuel pressure to ensure that it is not weak, would still be a good idea while you are at it!

I am replacing a fuel pump and the harness that attaches to the pump. I have to black wires that are coming from the harness, and the new connection has a black wire and a black wire with a white strip. what goes to what?

The thicker of the black wires is for the pump thin one for gauge.