B3: Check For Short to Ground

With connectors FC025, FC026, BT007 and BT008 disconnected measure the insulation resistance between FC026/013 and FC025/026.
3. Repeat for FC026/014 and FC025/026

Is the resistance > 10M OHM?

Yes
Go to B4

No
Inspect harness/connectors FC025, FC026, RH001, BT002, BT007 and BT008 for corrosion, damage, bent or pushed back pins. Repair as required and test the system for normal operation.