'88 300TE Alarm issue

[Merkey]

My sons '88 300TE has let us down twice with a dead battery. The car was parked for 2 days both times... but has been left longer before with no problems.
As soon as I apply the charger, the alarm starts flashing the lights... the PO had removed the wire from the alarm horn, so I assume this is an ongoing problem.

The battery is brand new.
I pulled up the pass carpet and shield and removed the lower larger connector from the alarm box after reading about that in a search.
I could not get the upper smaller connector off, so I left it.

Is that correct, or should I remove the upper too?