I looked this up for a 5.0 liter (305).  The other engines may be similar.  Let me know if your engine is different and I will double check if need be.

That system is controlled by a fuel pump relay.  The relay is mounted at the passenger side of the engine compartment behind the junction block.

I gets it's power from the ECM 10A fuse in the fuse box.  The feed wire is an orange wire.  That fuse feeds the relay, and the relay feeds the pump through a tan/white wire.

The relay is controlled by the ECM (computer).  When the key is turned on, it should power up the relay for 2 seconds, then shut down.  If the engine is cranked it will remain powered up, as long as a ignition signal reaches the ECM.  The control circuit from the ECM to the relay control is a dark green/white wire.  The ECM provides power to this circuit.   The ground for the control circuit is a black/white wire, and is always grounded.

In addition, when the engine is running, the relay is not on.  Power is supplied from the same orange wire to the oil pressure switch.  When the switch is closed due to the presence of oil pressure, the tan/white wire to the pump is supplied with power.  If the engine stops and oil pressure drops, the fuel pump is shut off.

There is a fuel pump test connector under the hood breaking out of one of the harnesses.   It is the same tan/white wire with a connector going nowhere.  The plastic on the connector is usually green.  The power  from the relay or oil pressure switch can be tested at this point, or the pump can be powered up.

Hope this helps.

Thanks for the help. Got the fuel flowing and the truck runs fine: but when I moved the truck it was dark- noticed I do not have brake lights ( have driving lights and turn signals just no brake lights) I have checked the bulbs, the brake fuse, and the brake switch. I'm sure they worked last year for the inspection. Does anybody have a brake light wiring diagram for a 1990 chevy truck?

The brake lights and the rear turn signals are the  same wires and bulbs from the turn signal switch out to the lights.   The turn signal is nothing be a blinking brake light.  The left one is a yellow wire, and the right one is a dark green wire.  Both 18 gauge.

The turn signal switch chooses.  The brake light switch feeds directly into the turn signal switch.

You have rear turn signals?  Be sure.  You can also turn on the 4 way flashers to check them out.  Again, same wires and bulbs, all feeding from the turn signal switch.  If the turn signals/4 ways work, then you have either lost power to the brake light switch, the switch is bad, you have lost the feed from the brake switch to the turn signal switch (white wire), or the turn signal switch has failed.

The turn signal switch failure is not likely, but does happen.  The brake switch is feed from a orange wire.  This orange wire comes directly from the fuse box, and also feeds the convenience center and other items.  It's a 15 amp fluse labled STOP/HAZ, bottom row center in the fuse box.

Thanks again. the color of the original wires really helped. This truck was butchered. My wire were not the original wires -when I connected the original wires it fixed the problem. I now have everything working "EXCEPT" the back up lights. The tranny is a 4 speed automatic - the connection is on the tranny but how were these wires run and what color was the original if they are found?

The back up light shares the turn signal fuse, turn signal  works, so thats good.  From the fuse the wire is dark blue that runs directly to the backup light switch.  It's a two wire open or closed switch, and does not ground, so if the wires are switched, it should work fine.

If you unplug the switch, and look at the harness connector straight on with the wires exiting the back, and the two bumps for alignment of the plug in the 12 o'clock position, the dark blue feed goes to your left.  The connector on the right is connects to a light green wire.  This light green goes body connector and continues directly to the backup light bulbs.  There in one more connector toward the rear of the truck, but the color does not change.

They share the same black wire ground as the other rear lights.

One of the advantages of teaching automotive in a tech college.  I have access to diagrams.

Well I found the problem (in this case the wire colors were correct for the length of the truck. I never drive after dark and this became obvious when I traced the wire and found the connection (blue/green) the shifter has been changed and the connections for starting in park/neutral was at the bottom of the steering column, placed in the neutral position and no connection to the replaced shifter which is now in the floor. This weekend I will be extending the wiring and placing the switch inside the console. All this trouble started when I decided to paint the truck and wanted to check everything and get it working before I did the bodywork and painting.Well anyway now everything will be working.

Thanks again. This site is better than any Chiltons.