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I have installed a new red color from the gray coming out of the fuse box and connected to the gray on the new pump connector as shown in the diagram that comes with the pump.

Furthermore, I have installed a new cable from the grounding point in the engine compartment and back to the grounding point on the frame, from this point I have added a new grounding cable to the pump connector.

When I measured the volt on the red wire that will provide power for about 2 seconds at the fuse box, I got 12.3 volts between this and positive on the battery, which should not be possible.

This changed when I unplugged the pump, because then I got 12.3 volts as normal for about 2 seconds.

So that's why I wonder if it might be the pump that has broken? It's an ACDelco.

Per

The entire truck frame is the ground for the entire system. As long as the main ground back at the engine compartment is clean ans solid then your frame is an exellent contact point for any ground. You need to remove that ground wire back to the engine compartment from the frame near the pump.

Why did you add a new ground wire from the pump to the frame? Did you remove the original ground wire from the pump to the frame?

You measured 12V between the battery positive and what red wire, located where?

George

The reason I laid a new ground wire was to make sure there is good ground all the way.

I added a new ground wire to the pump to be safe, and I removed the old ground wire.

I measured 12 volts between the battery and the feed wire coming out of the fuse box, it's originally gray but since I didn't have a gray wire I used a red instead.

I was out and measuring again now to be safe and then I measured between the prime connector in the fuse box and positive on the battery and had over 12 volts there when the ignition was off?

When we switched on the ignition it went down to 0 volts and then up to almost 10 volts for about 2 seconds and then back to over 12 volts when we turned the ignition off.

Per

Measuring voltage from the prime connector to the battery positive has no purpose. With the truck off that connector is connected through the pump motor windings to ground. The resistance from that connector to ground may be of value if a failed pump is suspected but that would be better checked at the pump.

Disconnect the new long ground wire from the rear frame to the front of the truck.

Make sure that your new ground wire from the pump to the frame is solid and has a clean connection to the frame.

Make sure that the old power wire from the relay box to the pump is disconnected.

Since your taking voltage measurements at the relay box, lets start there instead of at the pump where I suggested in post #18. We may end up back there later. Positive meter lead on the fuel pump prime connector and negative lead on the battery negative. What is the voltage during KOEO during the initial prime sequence?

George

Then I disconnect the new long ground wire as you suggest and measure continuity to make sure the grounding is good in the frame.

The old power wire is completely disconnected.

As I wrote above, it only went up to almost 10 volts at KOEO.

But I will measure again tomorrow after removing the long ground wire.

Per

You need to measure between the prime connector and the battery negative not the battery positive.

George

Disconnected the new ground wire, and the ground point on the back of the frame works properly.

KOEO - 12.3 volts in about 2 sec, but when we switch off the ignition it goes up again to 12.3 volts in about 2 sec

Only gets power at the primary connector, not the power wire that goes to the pump.

Measured between the postive on the battery and the power wire to the pump and then received 12.3 volts which should not be possible.

To be on the safe side and that the problem should not be in the fuse box, I dismantled the new power wire to the pump so that it is only connected to the pump, then still get 12.3 volts negative on this wire.

Per

How did you verify that the frame ground at the back of the truck works properly?

why do you keep measuring the voltage between the battery positive terminal and the power wire to the pump? This measurement has no purpose. As I said before, there are no negative voltages in your truck, only a negative reading on a meter if you reverse the meter wires. In this case the power wire for the pump is grounded through the motor windings of the pump with the truck off so it acts like a crappy ground with resistors and an inductor in the circuit. All measurements are with the black meter wire on the battery negative or a good clean frame contact point and the positive lead is on the positive voltage that you are trying to measure.

the pump priming terminal should be connected directly to the pump power wire. Why do you think that they are not connected?

you made sure that the new power wire is only connected to the pump. Where else was it connected?

once we straighten out how to measure voltages properly and what’s going on with these mew wires, we really need to get to the back of the truck and measure the voltages directly at the pump as I suggested many posts ago. I’ll hang in here for another couple of rounds but if you want my help I need you to follow my instructions. I want to help you fix your truck but You need to help me help you.

George

I measured continuity between the battery negative and the grounding point on the back of the frame and it was good.

I get 0 volts between negative on the battery and power wire to the pump at KOEO, only as I wrote over here 12.3 at the prime connector.

I use red on positive and black on negative, and if you change, you get the minus sign on the multimeter so it works properly.

The new power wire goes straight to the pump and is in the hose all the way so it is not near ground.

So that's why I think it's like you say, "In this case, the power wire for the pump is grounded through the motor windings of the pump with the truck off so it acts like a crappy ground with resistors and an inductor in the circuit" .

I get 0 volts at the back of the pump when it is connected, if I remove the connector then I get 12.3 volts between the rear grounding point and the power wire.

Per

See above. We need the test requested in post #18 to make any further progress.

George