ECM, Junction Box 3, +B and +B2 signals, wiring troubleshooting

Hi all, first post here so apologies if this is in the wrong spot or if there is already a thread for this.

Towing my boat last week, I felt a shudder and lost power to my 2007 4runner SR5. Water had gotten in the week before due to plugged sunroof drains. I suspected the ECM fried as this had happened before and we got this replaced. This time I wanted to diagnose the car myself and see if that's what it actually is, and if so if I can replace it myself.

Auxiliary power comes on, but I get nothing when I turn the key and my OBD2 sensor won't read anything. On the ECM, all the grounds tested OK. For power, pin E8-3 (BATT) and E8-7 (+ BM) had power with the key off and on, and pin E8-9 (IGSW) was 1.5V with the key off and 12.09V with the key on. However, E8-1 (+B) and E8-2 (+B2) had no power with the key on or off.

Does this mean the ECM is not receiving the proper power, or could it still be fried? It is supposed to get power to +B and +B2 from harness connector IC4 near the drivers lower kick panel, which splits off at junction 31 and 32 into +B and +B2. I am trying to trace this signal, but I believe I've incorrectly identified IC4. There is a harness connector near the floor that's very corroded so I thought that was it, but not I'm pretty sure that's actually connector IE1. IC4 appears to be up higher, but I need to confirm with wire colors. I am having trouble finding J31 and J32, black junction connectors with two rows of six pins, but if I find those I can check the +B and +B2 signal. What I really want to know is, should I bother or should this ECM be powering up with just the signal from BATT and +BM. Any advice is greatly appreciated!

I attached the diagram showing +B and +B2 splitting from the junction box into the ECM, two photos of the corroded connector near the floor that I thought was IC4 but is probably IE1, and a picture of what I now believe to be IC4 that is up higher (haven't taken this apart yet). They have the same pin profiles, but the assumably real IC4 (big black wire with yellow stripe top center) is upside down compared to the pin diagram.

 

Just to clarify a few things, the title incorrectly says J3 junction box. it is the J31 and J32 junction boxes, which appear to be clipped together in the diagram. I think these are to the right of the ECM, covered by bands of electrical tape. I plan to go to the junkyard tomorrow to pour through wires etc. and figure out what it what without having to worry about jarring something loose.

The main thing still is - should an ECM get 12V constantly from only +BM and BATT, or also +B and +B2. See the following Link:

Engine Control For 1Gr–Fe - Toyota 4RUNNER 2007 Electrical Wiring Diagram [Page 85] | ManualsLib

If you click to the next page, you'll see that the blue line (L is the code for blue) goes to the BATT connection on the ECM, and the black line goes to +B on the ECM. On the page the link goes to, you can see the blue line comes directly from a battery powered fuse, so it makes sense it is always 12V. However the black wire appears to only power the ECM (through +B and +B2 after going through junctions 31 and 32) when the EFI relay is closed (it is normally open) by the W-G wire, which comes from MREL on the ECM. This makes me think that MREL outputs a signal once the ECM is powered up, this closes the EFI relay, and then +B and +B2 are powered. This leads me to believe my ECM is dead if I am not getting the starter to crank, no reading on OBD2, all grounds on the ECM test good, and I am getting constant voltage on BATT and +BM (ignition either on or off), and IGSW (ignition on only)

Very little information about this stuff on the web