Usually top of gas tank since float attached to monitor level.
Should be on the top rear of the engine block near the distributor.
To fix the temp gauge check the temp sending unit first. A bad sending unit is a common problem with the temp system.
It is fuel injected.
In the fuel tank.
Bad gauge, stuck sending unit in tank, grounded signal wire
The fuel relay on a 1992 Chevy G20 5.7 liter, 350 is under the hood attached to the firewall at the top, just under the wind screen
You need to lower the fuel tank to get at it.
The fuel filter for a 1986 Chevy G20 should be mounted on the frame under the van. The filter is an inline type and should be easy to change.
The 1990 G20 Chevrolet Van fuel relay switch is located on the front of the fuel tank. The relay switch is next to the fuel pump.
In the throttle body.
I don't think there were any carburetors on the 1995 G20's so it is an electrical fuel pump inside the tank.
The fuel filter on a 1993 G20 van should be located on the vans frame. It is an inline type and should be easy to change.