I have a 98 Grand Marquis that is not pumping fuel. I checked the voltage at the inertia switch and only had 6 VDC. Underneath the trunk I checked the voltage at another connector and only got 3 VDC. Do you think I have a bad ground?
Check the fuel pump fuse. This is fuse 1, 20 amp, located in the under hood fuse box on the right front of the engine compartment.
Do you think I have a bad ground?
Why guess? You have a voltmeter, measure the voltage drop from the fuel pump “ground” to the chassis “ground” and you’ll know.
I assume that the voltage readings you stated were made using a good ground reference point. I also assume that the devices you tested are on the power lead side of the load. If that is correct then the trouble isn’t a bad ground but rather a bad connection to power. The fuel pump relay is a likely culprit. It would be nice to know where the 3 volt measurement was taken since the voltage is less than the first reading. If the 3 volt reading is after the load on the ground return side then there is a grounding problem also. A good ground point will be at zero volts when compared to a good ground reference point.