I spent all day thinking about this and i really think it has to be in the power feed to the fuse box or the box itself.... here is why:
Even when the gage is going nuts the voltage measured at the battery remains a constant 14.5....at least it did this morning when i was messing with it....also the starter and grid heater both function properly....both of them receive power directly from the battery not through the fuse box.....the only things that are acting bad are things that receive power through that box.
I wanted to mess with it more after work today but it did not act up
09 Dodge 2500 w/ a Cummins, dd/towrig
85 Toyota Pickup, 1tons, coilovers, 40's, ect