does that mean I have isolated the short and I dont have to worry aboout the short being further back towards the fuel tank.
No, it doesn’t really tell you anything other then what I already stated in my previous post. The problem isn’t on the fuel pump side of the relay. The clicking is due to the ignition side of the relay getting/losing/getting/losing power over and over again, which is flipping the switch inside the relay (causing the click) which sends power down to the fuel pump turning it on. Electrical pumps, like the fuel pump, don’t shut off like a switch. They need to spin down. So it may seem like it is running constantly if the power is being turned off/on fast enough. In other words, the problem is in the ignition circuit.
With that said, the ignition circuit is more then just the ignition switch. There is a bunch of stuff on both the positive & negative side of the relay, including the PCM, neutral safety switch, starter relay etc etc... You can narrow down which side of the relay is shorted with a volt/multi-meter.
first test the power side:
- Set your meter to as close to 15 volts without going under
- Unplug the fuel pump relay
- Key On, Engine Off
- Touch the negative meter lead to the negative battery post
- Touch the positive meter lead into the whole where the relay’s pin 85 went. The relay should have the pin numbers printed on it for easy reference.
With everything running fine, you should get a constant 12 volts. If the voltage fluctuates, then the short is between the whole your testing & the positive battery post.
If pin 85 checks out, next test the ground side of the relay:
- Touch the positive meter lead to the positive battery post
- Touch the negative meter lead into the whole where the relay’s pin 86 went
With everything running fine, you should get a constant 12 volts here too. If the voltage fluctuates, then your short is between the whole your testing and the negative battery post.
The next part (finding the short in the wire) is the tricky part if you don’t have a the circuit diagrams for your year/model truck. If you don’t, or don’t know how to read it, I would advise bringing the truck to a tech who can track it down for you.
Otherwise, plug the relay back in, key on/engine off, get a small compass and hold it over the offending wire. The needle will point in the direction of current flow. In a working circuit, on the power side, the needle will point towards the relay. On the ground side it will point away from the relay. Since the voltage is fluctuating on you, so too will the current resulting in the needle bouncing a little. If the problem was on the power side, then go south. If the problem is on the ground side, then go north. Keep going up the wire until the needle turns around. The short will be between the last place the needle was pointing in the expected direction and the first place its pointing in the opposite direction.