This subject has been introduced on the forum before under the name Battery Disconnect:
https://packardinfo.com/xoops/html/modules/newbb/viewtopic.php?viewmode=flat&type=&topic_id=15770&forum=1 As an electrical engineer having worked in the automotive industry on 6, 12, 24 and 48 volt DC electrical architectures, I suggest to always insert a disconnect switch or solid state device on the ground side of the battery supply circuit, regardless of whether Positive or Negative ground.
The primary reason for this is safety in that once shut off, any accidental contact between either post and the car frame or any other voltage ground reference will not result in high current. This method occasionally meets with challenge since almost all other switches in a car or any other transportation system are done on the hot side, but remember, this is simply done in order that individual functions can be turned on or off without turning others on and off. This is not the case for a battery shutoff in which case you want both safety and vehicle security.
Further, I recommend a switch with the highest current rating you can find. Otherwise, you will have a voltage drop that will affect starter speed and possibly, the ability to deliver maxium voltage during battery charging from the regulator. Yep, it will cost more, but the cheap ones available everywhere are cheap and everywhere for a reason.
The one shown in photos of my car in the other thread is from Flaming River. 15 years of use with no issue while still delivering fast start current.
Hope this helps.
Pat
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