Did you have a viper installed or one of the Direceted electronic ones??? Mine did the same thing when he installed it. They did what is called VIRTUAL TACH. If you read the directions for the install, it does not recommend using the virtual tach on diesels.
Once you hook up the tach wire it will work fine. Also pull the instrument cluster and its the top left blue wire 2nd from the end is the wait to start light. Most of the installers just put a 12 second delay on the start. That's way too long as the glow plugs can drain the battery down in that 12 seconds if they are weak.
Let me know if you need the instructions for the viper I have a 5902 and a 5904. Also if you go to
www.xpresskit.com you can find the instructions for the directed install kits.
My truck would try to start itself until it registered low battery and then it would stop. If I started it and let it run for 30 seconds, it would autostart just fine for the next 4 - 5 hrs then start doing what you described. Once the tach wire was hooked up, it works like a charm.
You may also want to turn off the dome light, set the alarm, wait 45 seconds for it to arm completely, then unlock and open the drivers door manually. If the alarm does not go off, then he hooked to the dome light wire and that also needs to be corrected.
My installer probably hates me, but he did both of my dmaxes and he fixed all of the things that I had issues with. Don't think he will ever put one in like he did my first install. A couple of cheap diodes and 5 extra tap connectors make a world of difference. Only adds 5 minutes to the install, but there is no way for the alarm to not work the way it was designed.