Another 12V Battery related issue....with a twist (and click)

[IMFletcher]

Hi -

I have a 2018 Fusion Energi Titanium PHEV.  It has ~45k miles on it and I've had zero issues with it since I bought it.......until recently.

 

I stupidly left the car in ACC mode which killed the 12V battery.  Couldn't get it to charge on a trickle charger, the battery is 6 years old so figured I'd buy a new one.

 

Did that, installed it and this is where it gets weird:

 

When I first connect the negative, the rear tail lights go on for a little while and then turn off.  Key Fob does nothing, turning the lights on via dashboard switch does nothing, pressing start button does nothing.

 

With the car in the "nothing is on" state and with the negative battery terminal connected, I hear a clicking from the fuse/relay box.  I've not been able to identify which one is clicking yet, but it will remain clicking until I disconnect the negative terminal.

 

I tried jumping the car, too, thinking that maybe I killed the new battery and same thing there - tail lights light up for a little bit, go dark and the relay clicking remains.

 

I've tried this with the HV battery connected and with the connector thingy behind the rear passenger seat removed and still the same.

 

Any thoughts?  Experience?