Headlight troubleshooting guide?

I saw an advertisement for a headlight troubleshooting guide. I was wondering if anyone on here had bought one, and if they found it useful or not. Seems kind of an odd topic for an entire manual, C3 headlights?

Semper Fidelis

I got one when I ordered a new set of hoses for my 78 lights,it's not a very big manual 5 or6 pages but helpful .

Here's a link that might help with this subject: http://vetteworks.tripod.com/techdocuments/Vaccum.html

I can't get the diagram image to open, but there is some good info in the article.