Decided to upgrade some of the old receptacles in my basement and garage with GFIs. After installing the GFI I used the test button on the GFI, reset, and then a Kobalt tester (see below) to confirm wiring and proper function.
There is a 240v 30amp double-pole breaker that feeds a small fuse box in the basement and then several circuits run off of it. I installed a GFI in the basement and it tested fine. The line then runs underground and into the shed where there is a 30-amp receptacle (never used or tested; previous owner had some heavy equipment) and several 15 or 20amp circuits in the shed and garage. There were two receptacle in the garage (separate circuits) and I installed GFIs for both. They both work, and when I press the test button on the GFI they pop. When I insert the Kobalt tester - I get the two yellow LEDs (right and center) indicating that it is wired properly, but when I press the yellow button on the Kobalt rather than the GFI popping the right side yellow LED goes dim, the center LED stays yellow, and the left LED lights red. The GFI does not pop. The label on the Kobalt indicates the LEDs to signify “hot and neutral reversed” and possibly “…missing ground”. I’ve confirmed the white and black wires are where they should be on the GFIs.
Same result in the shed though I didn’t verify which circuit the shed receptacle runs off of.
What’s the likely cause of the result I’m seeing, and will the GFIs operate as intended? If not - what do I do to resolve