Original "Shop Manuals"

[mckpaul]

I've seen "Original Shop Manuals" and/or "Unit Repair Manuals" for sale here and there on the net, ebay and car sites ets. In particular, the ones I'm wondering about are the ones for particular year model vehicles, such as 1984 Light Duty Pickups. They appear to be books put out by GM, have seen prices from $25 to $90 for them depending on the site or condition. Just wondering if anyone knows if you get more info in these than the over the counter Haynes or Chiltons books. Like wiring diagrams for example, I would assume they would be less generic and more specific in the original GM shop manual.

Have occasionally seen them specifically for my year model truck but hesitate to fork out the extra $$ without finding out if it's worth it.