Probably better off getting the later ECU, as cutting that wire does have side effects, such as the interior lights staying on for a few seconds after starting the car etc....
….but the guide is at http://www.omegaowners.com/forum/index.php?topic=90516.0
Zirks Mod does a better Job and gets around that, also fits Pre and Post 2000/1, does involve using a Relay as part of the wiring Mods. 
Pretty sure I posted up a Howto years ago, but just had a quick look and cant find it, it might still be sitting in the Test Section somewhere. 
I don't recall seeing that, and Jimbob is usually thorough about getting them sorted and moved when he has time.
Yea agreed, it was some time back (years) when I had my first 3.0 Plod, so that would have been 2009/10.
Dont know, anyway, bottom line is I reversed Engineered to one they fit to NonDBW Ex Police, but couldn't get it to work on the later 3.2's, so Modified the design, got it working on the 3.2 then modified again so it would work on both the 3.0 and 3.2.
Im sure I posted it up

probably still got the details kicking around somewhere, be it a few Hard Drives ago.