Mine (2) are wired to a positive buss bar(each on their own circuit) which is powered by a cutoff switch also. BUT, I dont just kill power to units using cutoff switch. I turn units off first, THEN kill power using cutoff switch. Haven't had any issues with graphs using this setup. Dont know if it matters but I liken it to turning off a computer first, then unplugging its power instead of cutting power WHILE it is operating. Don't know if it can cause issues with units, but, theyre too expensive for me to chance it. Turn unit off , then cut power to it. Just my 2 cents worth. Good luck.
'98 Tr20 Triton completly updated & rigged, 05 Magnum c-channeltrailer
'94 Merc 200Xri completly rebuilt & noseconed/low water pickup lower unit.