2007 gl450

Question

I am working on a 2007 GL450. The fuel pump is not receiving power, but upon initial start / crank, leave fuel pump relay and secondary fuel pump fuse which is 20 amp energizer's for approximately 7 Seconds. During those 7 Seconds the fuel pump does not receive power. I have read online that there is an inertia switch and I'm wondering where it is 2 diagnose this problem