OK. So think about it.
The S2 and J3 wires are disconnected from everything in the engine compartment.
When the key is turned to start, the light turns on.
Therefore somewhere at or after the key switch current is getting back to ground.
If the J3 and S2 wires aren't touching anything in the engine bay, then the pground is somewhere between the bulkhead connector and the key switch.
Does that make sense?