[mreid]

You will usually see around 12.8v out of a fully charged battery and that should be the same at any point in the system and around 14.2v when the engine is running and the alternator is charging the battery.

You've got a wiring issue, but I don't think it is ground related. Assuming you've already conducted a visual check, you can check it by disconnecting your positive battery cable and then checking continuity (resistance) using an ohmeter (multimeter) set on r x 1 between the negative battery terminal and as many of your ground connections as possible. Once you rule this out, use the ohmeter to check from the positive cable to the fuse box battery strip, then turn your key to "on" and check to the ignition strip. If all of that is good, it is time to check from each fuse to it's circuit. Time consuming, but it is the only way you will find a potential broken wire, miswired circuit, or pinched wire. Good luck!