Over the years I have bought and installed these kits....but it has been a long time ago. They were very common to show up in the `80`s at most Buick swap meets.
The kits contained 2 different jumper harnesses. There were also 3 hex head screws and clips to accept the screws when installing the light under the hood. There were instruction sheets which covered various years but I dont remember any Riviera specific instructions. I think the instructions may have been relatively generic.
One harness was to install the light in the engine bay. It had an in line fuse and pulled power from the stud at the firewall which directs power into the fuse box. I probably still have a couple of these harnesses laying around somewhere...
The second harness was for installation under the trunk lid. It was simply an orange wire about 2 1/2 feet in length which plugged into the existing trunk light power source and provided enough wire to locate the reel out trunk light in a central or close to central position. I dont think it is possible to locate the light smack dab in the center of the Riviera trunk lid because the depression in the center of the support ribs is larger in diameter than the feet of the trouble light. I remember fishing the jumper harness thru the voids created by the support channels and thru one of the oval holes near the center. I cant remember if the install was on the drivers or passengers side.
There is an early version of this kit and a later version. It is entirely possible, even probable, that the kits I was installing were a later version of the trouble light with different components and installation guidelines and not the same kit as Tom T. installed in his `64. I would note, however, that the illustration I posted above dates back to `64, albeit, a different model and not the Riviera.