Cool Pics I saw on Ebay
These pictures seemed like symbols for 8-track to me. They are similar in that they show the inner workings of carts.

That one is would be more symbolic if it had no text. This one is literal:

I think I have a xerox of that repair manual somewhere. It was made by Radio Shack back in the day. I don't think I have any completely clear 8-tracks, but many 4-track carts are half clear. I have about 25 4-tracks.