Welcome to the forum and congrats on your Hi-Lo. Lots of help available here, so you'll get the support you need.
Start by checking out the home page of this forum. There's a good collection of reference materials that will be useful. Look on the home page for the big red bars running horizontally, these are section headers. Scroll down toward the bottom of the home page for "LIBRARY" and you'll find a collection of Hi-Lo Owners Manuals and Hi-Lo Brochures. If you can't find an owners manual for your exact year Hi-Lo, just find a year that is close. Hi-Lo's don't change drastically year-to-year.
Just looking quickly, I see Hi-Lo brochures from the late 70's and early 90's. You may have to use those as your guides. I also see Owners Manuals from 1990, but didn't do an exhaustive search.
Here's a link to a collection of 32 excellent Hi-Lo videos posted on YouTube, showing the features and operation of most systems. Yours won't match exactly because it's over 30 years old, but you'll find it very helpful.
The "search" button on this forum is your friend, so don't be afraid to use it. Searching can be frustrating, but just keep working with it. Change words, reduce the number of words in your search, etc.
Post questions here when you have them. It's always helpful if you can post pictures related to your question. A picture IS worth a thousand words.