Many older cars/trucks have a fuel pump in the gas/diesel tank that emits RFI through the external gauge connections. The simplest solution is multiple ferrite beads on the fuel pump connection wires outside of the fuel pump. You may need to lift the car/truck to gain access to these wires. Use two FSB31-1/2 snap on beads on each wire (usually 2 or 3 wires depending on make/model). Works on boat fuel pumps also.