Extending the Cable for DEI 504D Shock Sensor

I have a full size pickup (99 Silverado Z71) with a fiberglass shell and need to install a shock sensor in the cargo area. I want to connect this to my existing Viper 3203 via the 4-pin mux input so I can have warn-away and full trigger. I tested the 504D by connecting it directly to the 3203, and it worked with both warn-away and full trigger. I then installed about 20-feet of 20 awg wire between the 3203 and where I wanted the 504, cut the harness and spliced the cable in place, connecting the red, black and blue wires. I connected the end of the harness with the jumper to the 504, and the other end to the Zone 7 Mux port of the 3203. Most of the time, when I arm the system, I get a zone fault beep a few seconds after it arms and the alarm will not sound when strike the side of the shell with my palm. Probably 20% of the time it will arm successfully, and will respond with a full trigger to a palm strike. Did I just extend this cable too far, or is there possibly something else going on? If I did extend it too far, what would you recommend for me to get a functional shock sensor capability there?

I've extended wires further when doing alarms in RV's. Did you solder or use crimp connectors? My first go to would be to check the connections that were used to extend the harness.

I have done the same with a Directed 508 sensor with no issues so I would check you connections