So I have done my best to research this topic. on my car I have been running the s5 alternator without wiring the S-terminal or the L-terminal FOR YEARS WITHOUT PROBLEMS. Im not sure why it worked but it did so I ignored it. Now Im getting a new alternator and I am sure I wont have the same luck. I have came across what I need to do. My only question is I cant figure out what I need to do. Im not sure what to do. My alternator is not its last legs and will probably make it 1 or 2 more days. Im switch to the FD alt.

This diagram doesnt make 100% sense to me.

 

I'll leave this here for you.

 

Ive seen that diagram. Its literally the first one that opens in google and in the search for this swap on this site. It does not help me.

I do not have the stock wiring harness, ecu, or electrical so there is no wire to the dash.

 

The ECU is not used (did you mean CPU).

 

I thought it was ECU. Either way I don't have the stock engine harness so I'm not sure what wire in the engine bay is the wires that go to the alternator.

 

And you have an S4? If so then the L terminal goes to the White/Black wire of the CPU's largest plug. The wire is found above the Blue wire and next to a Green/White wire (the W/B wire is part of the front harness). The S terminal can go either to the engine fuse box and tap into an existing fuse there or you can use one of the empty slots or the wire can go directly to the battery with an inline fuse.