ES to I swap wiring question for 13 button OBC

[e28m5]

I have a recently purchased 325es that was swapped to an I and i noticed that the code function and the mph function do not work. I read a ton of posts on here about the swap and everyone says that if you have the 11 button you need to splice in the yellow and white wire at the dme and the black wire to the instrument cluster. it seems that everyone says if you have the 13 button you need to also splice a 3rd wire but i cant find anything about which wire it is. Has anybody done this swap with a 13 button OBC and know which wire needs to be spliced to what? Any help would be greatly appreciated. thanks

[Gooch]

Bump for a new e30 owner.

[MR 325]

I had an 85 325e with full OBC. I swapped to an i engine using an 87 iS engine harness. I spliced NO wires for the OBC and it worked perfectly.

[e28m5]

Hmm. I wonder if my code function in the obc is just not working.