Hi,
Check this out ... Good Luck!
msikdm
http://isuzufaq.ibctech.ca/#faq26
The alarm goes off randomly:
Rodeo: It's the tailgate switch. Open the door, take off the 2 Phillips head screws that hold the pin switch on (the one that controls the light) and stick two or three washers behind the switch under each screw.
Also check the hood pin: It's by the ABS module over the pass side front fender well on the 1998+. The pin is covered by a rubber boot.