I'm doing some maintenance on a Rickenbacker M-8E (single-ended from '57) and I want to make sure that I'm safely grounding things. Is there way to test with a multimeter? For instance, I've grounded the three prong plug as Gerald Weber suggested in one of his videos, by soldering to a lug secured to the chassis by one of the PT screws: In this next picture, I've removed one of the old bypass caps and soldered the new one to a little piece of the old one that connects to ground. I knew I wouldn't be able to solder directly to the chassis, so I thought this was just as good. The joint seems strong, but is there a way I can test it? Also in this picture are the two new filter caps which I soldered to a lug connected to the OT. I realized later that the lug is not touching the chassis, so I need to fix that, but in general is this a method that could work? Again, can I test for good grounding before actually plugging in the amp?