The ECU is located under the passenger seat, located under a black rubber cover. To remove the ECU, the front seat must also be removed. There are two electrical connectors that must be disconnected to remove the ECU. There is a latch in the center of the top of each connector that must be depressed before you can work the connector out. A flat-blade screwdriver is pretty much a necessity.
Once the ECU has been removed, you end up looking a silver box as shown in the picture, below.
The wiring harness plugs into the two white connectors on the front. The two round holes on the right side allow access the idle mixture adjustment pots.
...And that's all there is from the outside. Of course, all the interesting stuff is on the inside. Fortunately, disassembly is easy.