Backline equipment (e.g. guitar amps) is notorious for having been hacked, modified, DIY'ed and left in unsafe condition. Close inspection is essential, take nothing for granted, keep an eye out for alterations to earthing e.g. retro-fit earth-lift switches. Other than that, treat like any other electronic equipment. Don't use signal connections to pick up an earth test point on class I. If multiple pieces of equipment are interconnected, preferably remove signal interconnections before testing earth continuity to avoid test current circulating, otherwise use low current test to avoid damage. Don't be 'soft' on it, it's no more sensitive than tellies and PCs.
