[JamesM3M5]

So I think I found the root cause - MAYBE.

Had a customer come in with an N55 with JB4, Burger OCC, intake, etc. Car was formerly owned by another customer. Water pump just this week began to run on after shutdown to the point of killing the battery within an hour or so. Witnessed it myself both times I ran the car up front and shut it down and when I brought it into the shop and shut it down. Pump came on both times within 30 seconds of key off.

Removed the JB4 completely, and the problem was gone. Then I searched and found this thread. There had to be a problem causing this to arise after being tuned with the same JB4 for years.

So I disassembled and cleaned up some of the hack fixes and updates to the original harness. The wiring harness for the JB4 is, to put it diplomatically, amateur. Additionally, the previous owner must have done some work because there were 2 wire nuts to install the fuel pressure rail sensor intercept, cheap crimps, and a mix of tapes. The wires going to the rail fuel pressure sensor were bare, and large sections of wire were unsheathed. Fixed all that with proper crimps, moisture-seal heat shrink tubing, and plain old Scotch electrical tape.

Then I found massive corrosion inside the 2-pin connector for the boost control solenoid. The connector sits upright and allows water to run right down into the back of the connector, since there is no boot, no tape, no seal on the wire side of the connector. I took a wire brush to the pins in the solenoid and picked out the corrosion off the contacts inside the plug on the JB4 harness. Wrapped the boost control solenoid plugs with high temp silicone self-adhering tape to keep water out. Voltage and signal degradation are a huge problem for modern electrical systems and cause major headaches trying to diagnose.

Test drove the car and cycled engine on and off many times. Water pump no longer ran on. So I put the power wire from the JB4 back under the 50A fuse (a rather questionable way to get power, IMHO), and the water pump still did NOT run after shutdown. I'm not 100% sure that was the all-out cure for this car's issue (along with CELs, half engine, and other sporadic codes), but I will follow up with the owner on Monday to double check.