I still say shouldn't be an issue. The OEMs don't like multiple wiring harnesses because it's cheaper to buy 10,000 harnesses that do everything then leave the plugs for options that aren't on the car unused, than 1000 with this set of options and 1000 with that set of options. It also makes it easy for the dealer to sell that option to you in the future, with a very high markup due to the need to "wire in the accessory." At most, if for some reason your LS can't handle it because the plugs are different, swap the plug ends between the cars. Tape off the extra wire on the one you're trading in, and jumper the power lumbar off the power line for the seats. No need to worry about the load, because you aren't going to be adjusting both the lumbar and the seat motor at the same time and the seat motor is going to be the bigger load anyway.