I bought a box of LED florescent T8, the kind that directly replace regular T8 bulbs, no wire cutting required. I replaced a couple of dead and dying bulbs. I liked the brightness so I thought I would replace all the bulbs in my garage which is completely lit with florescent shop lights. The first four bulbs in a light worked great. It was much brighter than before. Then it was a disaster. Some lights are very dim, but all 4 bulbs light, after the replacement. For other lights, some would not light at all or just one or two bulbs would light. And I have a couple of lights where 3 bulbs will light, but not 4. How do you troubleshoot whether it is a tombstone or ballast? I have a multi voltage meter, but I can't get anything to show on any scale I select? Any other advice? Are there ballasts that work better with the LED bulbs?