its the charge harness that connects to the starter, fuse block, and battery. i have an s5 harness that looks clean, is it the same ? can i just swap them out for each other

 

For the S4, there are 4 different engine harnesses listed. Two different turbo harnesses, one w/o turbo MT and one w/o turbo AT.
For the S5, excluding the turbo, there are 5 different engine harnesses listed. AT w/ air bag, AT w/o airbag, MT w/ anti-lock w/ air bag, MT w/o anti-lock w/ air bag and MT w/o anti-lock w/o air bag.
So, there's a number of different engine harnesses between the S4 and S5, and there are a number of harness variations just for the S5. I would say that your chances of matching an S5 harness with your S4 harness is slim. I would say, the only way to be sure, would be to lay them both out side by side and do direct comparison. I do know that the dash harnesses are different for the S4 and S5, and the dash harness plugs into this engine harness. Your best bet would be to buy a harness from an S4 for your S4.

 

the connector that goes from the charging harness to the body harness is different S4 vs S5. the S5 uses 1 big plug (?) and the S4 uses 3-4 small ones