Someone explain a shunt please

[memo43]

Ok as I'm going through my fuse box and trying to clean up some wiring.
I've discovered a fuse labeled "shunt".
Not knowing what it is or what it does, can I remove it and tap into it with a spade terminal to power another source.
Forgot to mention the truck
I'm working on a 85 chevy k20
thanks in advance

Memo

[Accelo]

What truck are you working on? The fuses for the shunt (amp gauge) is not fused in the fuse box but in the harness on 67-72 trucks.

As electric current flows through wires their is some resistance to the flow.
So if you measure voltage on a long piece of wire the voltage goes down as you move further down the wire. A shunt runs most the current along a wire and measures the difference in voltage along two points on the wire. Since the length of wire used is short the voltage drop isn't much. So the gauge in the dash is marked (Amps) is in reality measuring mil-volts of voltage drop. the gauge is really a sensitive voltage gauge.
This allows the manufacture to run a smaller wire diameter into the cab that would otherwise be possible. The short fall is any additional resistance, anywhere in the circuit, will throw the mill-amp gauge off, or typically it will not work at all.

The additional circuit resistance is responsible for 90% of the gauges that are not functioning.

The issue with small changes in resistance changing the gauge function is why "GM" went to a voltage gauge.

[memo43]

Thanks for the reply as well as image.
I'm working on an 85 k20.
I was testing various terminals and what not
but I think everything that I'm having issues with are more likely related to weak grounds.
I have my work cut out for me this up coming weekend.
going to upgrade from the factory 16/14 gauge wired to 10 or twelve, most at the headlight plugs.