Power used to pass from the alternator, into the cabin, through the amp gauge (where 12volt power is spliced off) and back out the cabin to the starter relay where it provided charging to the battery. If you break the loop, then you are losing your 12 volt power source. The ideal with removing the amp gauge is to connect the two wires (red and black) that ran to the amp gauge originally. After connecting those, they are now you constant 12 volt source. A splice comes off of that for the fuse panel, keyed sources, etc.
If you have already done that and you still don't have power, check the fuseable link. You may have accidently shorted it out.