Update Viper alarm & remove remote start

Hi there... new user here I recently bought a 2003 Nissan Xterra (manual trans) from original owner.    Low miles, well maintained, this was someone’s baby. Included a Viper alarm with all bells and whistles that seemed cleanly and probably professionally installed. The problem with current Viper setup is crappy 2003 era remotes. Both are bulky and not functioning when I bought it. For the same price as a replacement remote, I could just upgrade the whole thing to new electronics. I’ve found the following under the dash: 771xv alarm with remote start 5080 motion detector Xcrs 500m relay I’d like to remove and install an updated, basic VIper 3105V 1-way alarm. I have no need for 2-way, and I don’t need or want remote start (esp on a MT truck). Here’s the questions 1) Can I DIY this or am I better off going to a shop? I just want the car to start&run&drive. I don’t want shorts or electrical problems or the car shutting down on freeway. (I’ve been there before, don’t want to again). It’s the remote start unit that concerns me. 2) if DIY, can I reuse the wiring harness from old alarm to the new one. I think so: they fit together, wire colors are the same, just need to add one wire to the 12v ignition. I will have to run some new wires to antenna, valet button, etc bu these seem ok. 3). More importantly, can I unplug the harness to the XCRS 500M relay unit and leave it alone.   I don’t want to mess with the ignition, starter, etc wiring. It seems well installed and I’m more likely to mess it up than just leaving it alone. Maybe I’ll tape it up and leave a note for the eventual next owner. 4) can I reuse the motion detector? I wouldn’t pay for one but I’ll take it if it’s free. Thanks for advice. I have ok DIY skills but I’m no pro mechanicSent from my Apple IIe

From what you wrote the answer to all your questions would be a guarded yes. Before you connect wire for wire, test and join with soldering and heatshrink sleeving please.

Trigger wire from motion detector to go to blue (trunk trigger) diode separate. Here's how. A43_diodes.bmp

Thanks for the help... this worked beautifully. Replacing the 14-yr old old Viper unit with a new one was a matter of swapping the CPUs. I just had to run a few new wires, it it was mostly plug n play. I was lucky that the original unit was cleanly and professionally installed. I double checked the connections, but they were soldered, heat-shrink wrapped and zip tied in place. I also found that the PO also paid for a battery backup, along with remote start and motion detector. I’ll have to test the battery this weekend, but I hear the batteries don’t last long. Thanks again for the confidence booster to do it myself. Got me thinking about some other electronic projects. I’ll be around this forum for a while.Sent from my Apple IIe