I have a head unit from the US Pioneer P9800BT. My car has the a
harness that does not plug direct into the head unit.

The head unit has lots of cut wires that have the -

Rear Left Speaker: (+)plus
Front Left Speaker: (+)plus
Front Right Speaker: (+)plus
Rear Right Speaker: (+)plus
Rear Left Speaker: (-)minus
Front Left Speaker: (-)minus
Front Right Speaker: (-)minus
Rear Right Speaker: (-)minus

etc etc etc

My harness is the standard ISO Mercedes A class and i have the harness
diagram -

Title: The wiring connector by the side of vehicle.
(The figure seen from the vehicles coupler side)
+------------+
| #1 #2 #3 #4|
| #5 #6 #7 #8|
+------------+
| #9#10#11#12|
|#13#14#15#16|
+------------+
---
#1:[Peach]:Rear Left Speaker: (+)plus
#2:[Brown/Green]:Front Left Speaker: (+)plus
#3:[Brown/Red]:Front Right Speaker: (+)plus
#4:[Peach/White]:Rear Right Speaker: (+)plus
#5:[Brown/Peach]:Rear Left Speaker: (-)minus
#6:[Brown]:Front Left Speaker: (-)minus
#7:[Brown/Black]:Front Right Speaker: (-)minus
#8:[Brown/White]:Rear Right Speaker: (-)minus
---
#9:[Peach/White] Power source of Accessory
#10:[Oxford blue/White]:Antenna Remote
#11:Null:Null
#12:[Green/Black]:Vehicle Speed Signal
#13:[Brown]:Earthing
#14:[Ash color/Black] :Illumination
#15:[Peach/Blue] Power source of Back Up
#16:Null:Null

My question is how do I hook up each wire in the relevant hole? DO i
need to solder it on or can i stick each wire in the relevant slot?