I spoke with Isuzu techs at the dealer regarding installing an aftermarket alarm, and they highly recommended against it. All kinds of problems with vehicles not starting/running right/intermittent running etc. after install. Most alarm installers tie into the existing factory system instead of a fresh install which would be in addition to and not instead of the factory alarm. And since the alarm is part of the on board computer now, all kinds of bad things may be possible even with the uninstall of the aftermarket alarm system.

'99 Trooper, 912's
'89 Trooper RS, 2.6