DIY OBD2 trickle charger

I'm building a solar trickle charger with a 10w flexible panel I had kicking around my junk pile, an Ecoworthy EW1907-30A 12/24v PWM controller and an OBD2 to cigarette lead.

This is for an old Renault Kangoo Mk1 from 2008.

I will be adding inline a 5A fuse.

On inspection of the OBD2 lead, there are 2 inputs (+ and COM, on a standard cigarette plug.

The OBD2 plug has the hot as Pin 16, as expected. GND is Pin 4 & Pin 5. Pin 5 is Signal GND not Power GND so I don't really want to use it. All other pins are tested and not connected to anything.

Can I just physically cut off pin 5? I don't want to wreck the OBD2 connecter if that's not a good idea but I think I only need Pin 4 and Pin 16.

(I am aware of better alternative connection methods but these are all leftover bits n bobs and I do love tinkering about with stuff I really shouldn't)