If I could suggest, a master switch is more convenient when you need to cut power at the source to do some work safely. You can work on it without messing about taking the battery out. In addition [and apols. to long-time forum members who've heard me beat this drum multiple times] it serves two other vital purposes:
1) Theft protection;
2) Prevention of the most common cause of fire in old vehicles - short circuits. I turn the switch off any time I leave Matilda for more than a couple of minutes. When I park her in the garage (which is under our bedrooms) it goes off, too.
As to 1), Whenever I leave Matilda while I'm shopping, etc., the key comes out (it just lifts out) and goes in my pocket, alongside the ignition key;
Re. 2), I was impelled to installing the switch when I was driving some 25 years ago and noticed Lucas Smoke emerging from under the dashboard. By a lucky chance, I had my tools with me and was able to get the negative (ground) terminal unbolted and removed in under a minute. Otherwise, I might have stood there, like one of our forum members, and watched my dear restored Matilda burn to the ground. An unfused line to the light switch had worn through the firewall grommet and grounded.
Some members have installed cutoff switches far away from the battery, which is - excuse be for being blunt - dumb. It needs to be right at the battery post. Otherwise you have feet of unfused and unswitched primary cable, capable of carrying 500 amps or more.
Pic showing the top of the switch that emerges from the battery lid and carpet, with key in and a nice chrome bezel that I found that fits well. I can reach around and turn the key off without leaving my seat.
