If you inside gauge is analog (has a needle) and your hand held is digital (numbers) then the hand held will not react fast enough to fluctuate like the gauge.
You should always take an electrical load off the alternator output stud, not the battery post.
I'll bet your MSD is making hr gauge jump around as it's a heavy draw that is constantly turning on and off.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
