How to ,remove electrical connector from IP

[Dagwill]

Zd30 engine wont start
Tried to remove connector from IP so i can test # 7 for voltage.
How does this plug come off. I see a 20mm x 40mm grey plastic part that i can slide out towards me 20 or 30mm as im hanging over the guard. [some sort of locking devise, i think]
Not sure what to try next , any ideas thanks

[Dagwill]

Some joy, apparently i didnt have the slide release quite far enough out, once i got it the plug removed rearwards easily.
Plug connfiguration was a little different to the one shown in the manual. similar but 6 connectors Vs [9 in manual]
connector that would have been closest to me and on the bottom gave me 12.6v and the one above it went to ground. So i think thats ok, starting to worry its the pump.