Do you have a recommendation for a tester?And the installer is long gone. A $50 panel tester is a smart investment when buying something from the back of a truck. Using a voltmeter and current clamp are a poor way of testing. I'd build a tester with two 100W incandescent lamps in parallel to put some load on them. Bypass diodes are usually about every 8-9 volts. With a diode or two shorted, those numbers would make sense.