When I had my restoration shop open I was also an authorized CrimeStopper dealer/installer. Alarm systems are incredibly easy to install. Consequently they're also incredibly easy to defeat as well. But, it gives most peace of mind and on some occasions an insurance discount. In any case, to make life difficult for any would-be thief, you can fab your own wiring harness out of a single color wire. All you need to do is get a spool of whatever color wire you want in the same guage and type (stranded, solid etc.) as the original harness. Then take some masking tape and put a tab of tape on each end of each individual strand. While you've got 'em separated mark each end of each strand to correspond with the colors and/or markings of the original harness. After installation and everything tests okay remove the tape tabs. Then if someone knows to just cut the "blue wire" or somesuch they'll be royally screwed when trying to jack your ride and move on to the next. Time is money! This is also a great technique to use if you do your own home security systems, but only if you hide the sensors and not place them in plain site like most installers.

Anyway, there's my $.02!