Last update: Mar 21 2014
The IC engine block itself forms part of the electrical circuit. It has several ground connections, one of which is for the fuel level sensor, vehicle speed sensor, and the instrument cluster. With the IC engine removed, these connections need to be replaced. I recommend grounding these wires at the connector nearest the engine (F60 in the diagram below).
I recommend leaving as much of the existing engine wiring in place as possible. In order to remove the clutter of the engine wiring harness on the passenger side of the engine bay, I removed the wires all the way back to the ECU and removed the ECU itself. It was a decision I came to regret. I cut off the connectors to the ECU only to find that some wires unrelated to the IC engine are spliced together near the connectors to the ECU. Thus, I inadvertently severed several important connections. Additionally, it would have been much easier to identify wires leading to the ECU with the connectors still attached.
One problem that resulted from removing the ECU was that the keyless entry unit malfunctioned. This was perplexing and time consuming to diagnose. I eventually discovered the culprit was the immobilizer control module, which was not happy without the ECU. The problem was solved by disconnecting the immobilizer. The specific problem is that the immobilizer produces 10V on pin B141-26 (WR), which is connected to the key warning switch B370-2 (WR). This connection is not shown in the service manual wiring diagrams. The immobilizer pin B141-8 (Y) is also undocumented.