The reason this is important on a car installation as there is usually alot of metal objects around the battery terminals. By disconnecting the NEGATIVE TERMINAL first then you may have less of a chance or sparking a wrench or something touching the POSITIVE TERMINAL.
The RV Trailer battery terminals are most often all out in the clear where this is not a problem accidentally shorting something out. In a tight spot Battery cable installation I always remove the NEGATIVE battery terminal first.
There is no electrical reason why the NEGATIVE or POSITIVE terminal is to be removed first.
Just a shade tree mechanic's tip...
Roy Ken
