I'd like to be more help but my wiring diagram shows the CTS as a two wire sensor/connector,

Wire colours are terminal 2 brown and terminal 3 pink.

I've come across this type of sensor before,

one side sensor signal to the ECU,

and the other two pins feed eventually to the gauge.

Though from your description there going to be hacked up wires in the harness somewhere.

In this situation without reference to a genuine wiring diagram I'd buy a S/H plug plus as much of the wire harness as I could scavenge from a breakers.

Then into the wiring harness and find where the last idiot cut the thing and then splice S/H plug into the harness.

Heat shrinking and insulating as you go.

I have looked at a genuine Vauxhall wiring diagram for this van,and there is no evidence of a 4 wire coolant temp sensor in the circuit. The reference to the part on e bay ,if you follow the listing,is not suitable for your vehicle.(looks like a VW part to me).Some one has obviously been playing here,so needs to be sorted by a competant techy.