1) ABS was an option, not standard equipment in 1991, though all '91s apparently use the same master cylinder with a level senser in the reservoir. Sorry that I cannot speak to the 1992 model.

2) If you have ABS, you should notice a short buzz the first time you drive forward after starting the car. This is the ABS self-testing.

3) Though I have never seen a 240 ABS module, you should be able to easily find it. It should be a fairly large module with two hydraulic lines in and four hydraulic lines out, and at least one multi-wire electrical lead attached to it. Follow your brake lines from your master cylinder. They will either go to a large ABS unit (bigger than your fist) or to a small metal block about the size of your thumb with a single thin wire going to it (the brake failure warning light wire).

If you do have ABS and it has failed, you may want to consider just leaving it alone rather than investing in fixing it. It is sort of like your air bag, nice to have when it works, but probably not worth the $$ to replace.

If you really want to get it fixed, there is a guy in southern CA (Rocha, I think is the name) who rebuilds ABS units. He did our S70 and it works just fine. I don't know if he does 240 ABS units.