Fuel Gauge Issues

[1974ChevyC10]

last tuesday i replaced the starter on my truck.while i had it out i replaced the old nasty looking positive battery cable with a new one.well the old one had this j-shaped bracket that bolted to the fuel pump plate on the block and these 2 other brackets that held wires.well when i hooked up the new cable without any of these brackets and went to go start the truck the fuel needle moved halfway past the f mark.im not sure why the hell it did that so im asking you guys since i cant get a straight answer out of anyone else about this.one guy i work with says i should check the wires coming out of the fuel sending unit in the tank and my dad who has stuff to test wires and what not which i dont have well he is harder than hell to get anything done with.i wonder if maybe that bracket that bolts to the fuel pump plate could be a cause too since it didnt do this until i changed the old cable.all of the cables and wires by the starter too are out of the way of the exhaust as well.any ideas