Log on to Cummins' website and create an account to get service information for your engine, including component locations. You'll need the serial number. If memory serves (a dubious assumption at best), the ECM is located under the injection pump on the passenger side of the block. The serial number on an ISL is on the passenger side, on the top of the (timing cover?). It's hard to see but easy to take a picture with a cell phone camera.
1976 Southwind 28', '96 Winnie 34WK,
2006 Tiffin Allegro Bus 40QDP