Originally Posted by barndoor
Also, not sure if it matters, but with the key "on" I get 12 volts at the harness for 1 second and then it drops to around 6 Volts which i assume is the relay doing it's thing.
Fuel Pump Monitor (OBDII):
When the fuel pump is commanded on
by the PCM via the FP relay, the PCM monitors the voltage on the wire from the FP relay to the Inertia Switch to make sure that the relay is working. Should be near normal battery voltage
When the pump circuit is commanded off
via the relay, the PCM supplies a voltage to that same wire to check continuity through the Inertia Switch and then through the fuel pump to ground. This is probably the open circuit 6V you are seeing. When the circuit is complete, the voltage will be pulled down much lower than 6V by the path through the pump to ground. The voltage level is used by the PCM to make a judgment about the integrity of the circuit.
I don't have the exact thresholds but it could be something like this:
Low voltage within a calibrated range => circuit OK
Voltage hgher than calibrated range up to 6 volts => open circuit
Zero or near zero volts => short to ground