battery(stock Motorcraft) is 34lbs, tray is less than a half pound,22ft 2ga wire is 12lbs(for run to rear),16ft 2ga wire is 8.75lbs (for alternator kill switch) 8ft 2ga wire (for starter to relay box) is 4.25lbs(all weights include stainless cushion Clamps every 12 inches) as weighed on my scale at home(digital Bathroom Scale) so you save 9lbs not much really after you look at it, Kinda sorry I did it to mine but needed the room up front. also remember your putting it back in the car (better for traction) but your not really losing weight your actually gaining the weight of the wire and hardware.
I used all Marine grade UL and Coast guard listed Wire(I do this for a living) and used flex-loom and Stainless cushion clamps every 12inches per ABYC Codes.I also used a 150amp Breaker which was not weighed.
stock passenger seat(cloth,Manual)is 44lbs gone (for real)
if it didnt help Pro cars would prob have them too.aftermarket h pipes also save alot of weight.(offroad)more if you get rid of other crap you dont need if you get rid of cats(smog pump etc)