After changing to a new loom which required a change in alternator oil pressure and water temp plugs I have found when turning he key to the ON position the starter motor is engaging and trying to start the engine? HELP

I had the same problem. Can't remember exactly what is was but I hooked up some wires wrong.
Try disconnect the smaller wire that plugs in the side and see what happens 

Small wire to what?

Scott
Small wire to what?

i think dasic1 might be talking about the starter motor solenoid wire.
 
 

If that is the round terminal ended one that us a white wire I have tried taking that off but found that I couldn't get the starter to work at all.

the white wire with a ring terminal goes with the big black and red one from the battery.
 
there should be a black and white wire going to the solenoid

 
 

I have tried with the solenoid brown plug disconnected and then with the ring end wire and both ways prevented the starter from working at all. I am not sure what else to do. Might be time to call an auto electrician.

I have removed the cold start injector could this have an impact?

a bit of background info needed mate, this new loom you put in, are we assuming engine loom only, or body loom also?
 
is there anything modifed on the loom apart from changing the plugs you did, has anyone hacked some up and modified some wires, or better yet, did you swap because you old one was hacked out with some dodgy wires.
 
the only way the starter would crank when the key is turned to on is is somewhere along the line the STA line has been spliced to the IGN power. do you have an aftermarket alarm system? the guys who install these are butchers and hack the STA and IGN lines usually.
 
Start at the begining of the circuit, check out the wiring behind the ignition barrel, make sure the STA and IGN aren't exposed or touching. then follow through to the relay, make sure that checks out. If you have a multi meter you can check continuity between the STA line and the IGN line see if they are bridged anywhere, disconnect plugs to isolate sections to locate the bridge.

Engine loom only. I swapped because old one was hacked up. Yes after market immobiliser. It was not an issue on old loom and I changed the required plugs first then made two changes on the ecu plugs to mimic the old loom because of the issue. I am out at work for two weeks now so am going to have to wait till I get home.