S4 ABS Warning light triggers
 

I recently attempted to install a standalone into my 88 GXL. Things didnt go as planned so I put everything back together so I can drive it stock while I think about my next plan of attack. This involved reconnecting wires on the stock harness but as far as I'm aware. None that would have affected the ABS system. Regardless, once I started the car again the Anti-lock warning light always comes on soon after starting the car. The ABS seems to be working fine. My braking feels no different. The only thing I did to the computer was unplug it briefly while trying to removing the ECU for the first time. Anyone have any ideas on the cause or fix?