You should always run the power for your refrigeration
compressor right from the unit to the positive and negative terminals of the battery, preferably battery terminals that DO NOT have anything else connected to them, like alternators, battery chargers, inverters or other heavy loads. The No 1 troubleshooting issue is electrical on these Danfoss units so do everything you can to eliminate it. Also...don't skimp on the electrical wiring
in 14 or 16ga wire....ahhh...I wouldn't use anything below 10GA wire even for the shortest of runs. You want to shoot for less than 5% voltage drop when you consult the wiring size vs length chart.
Here is an electrical troubleshooting video and even if you have a different brand of unit, the troubleshooting for electrical is the same. At the 3:35 minute mark the error light discussion starts. At the 11:50 time mark, the 3-flash error code is explained along with troubleshooting for it.