Electrical – How to get the fluorescent 4-tube under-cabinet lights to come on reliably

The basic problem is that the occupancy switch that you chose to purchase is one designed to be able to work in series with the load attached to it. If the attached load is too small (too low of wattage) the switch assembly does not get enough power to operate correctly. For the particular model you have this is on the order of 40 to 50 watts of minimum load. From a technical standpoint it kind of sucks that they work this way BUT they are designed to work in place of a simple light switch that is in in series with its load.

Your Radio Shack relay does not come close to representing a 40-50W load on the switch so the only other way is to add some additional load in series with the switch (i.e. equivalently in parallel with the relay coil). As you have come to see this is not a very satisfactory solution and some other scheme needs to be found.

The best situation in this case is to acquire the alternate type of occupancy switch as mentioned in that thread that you linked. That type of switch has a live AC lead and neutral AC lead connected to it to power the switch unit irrespective of the size of the load. A separate output connection goes off to the load you are trying to switch. This type of switch may take a little re-wiring in your garage but that should be easier than trying to wire in the kludged extra load that the current switch requires. If you choose to deploy this improved version of the switch you will be able to remove the Radio Shack relay from the installation.

To make yourself feel better about the fact that you now have an extra occupancy switch you could pick a room in your house that has a tendency to get its light left on accidentally and install the extra unit in place of its light switch. Maybe this is a bathroom the kids use or a far closet that does not get used often.

BTW

It looks like Leviton now has a whole slew of different model occupancy switches that are also designed for single pole switch replacement but have removed the minimum load requirements. These do not require a neutral wire connection but do require a GND wire connection.

1. Confirm your wall switch is good. Bad switches can be intermittent.
2. Turn off the switch and take the tubes back out and put them back in making sure they're fully snapped in. It's worth a try. Don't go buy more, but if you have other new tubes try them.
3. If the lights work for a period of time and go out on their own, that usually indicates an over-heating ballast - replace the ballast.
4. Otherwise, the best test for a ballast is just what you did, try new tubes. If no luck, replace the ballast.
5. While replacing the ballast, make sure all of the wires in the sockets are well connected. Give them each a little tug. If you can't get a wire to stay in a socket replace the socket, maybe replace all 4.
6. Fluorescent lights need to be grounded to work properly. Make sure a ground wire is attached to the fixture. I've seen fluorescent lights, especially in old homes, where the people say they're always replacing tubes, and it's because the fixture isn't grounded.
7. If you're going to replace the ballast or the entire fixture consider going with an electronic ballast maybe even T8 size tubes. Amazon sells the smaller clips you'd need for a retrofit to T8 U-Bent tubes - ASIN B00A3WGR0W.