Can't suggest a lot, but code 12 you can ignore. There should be a cut through on the engine loom for TPS - both this and the rpm signal tap should trace to somewhere in the loom, so start with finding the connection to each and tracing where it actually goes.
Theres a good chance that the plugs are just from the loom themselves - It might be useful to check what the wire colours in the back of those plugs are if you can't find any other info - PJPJ had a load of info on the site linked in his signature, but I can't get it to load at present properly - its worth a look here if its working again (theres some schematics there from what i remember, the EGI ones aren't particually helpful, the GSI ones slightly better).
http://homepage.ntlworld.com/paul.joyce ... ystem.html
Based on what i can see from the pictures I'd suspect one of those is the injector cut circuit as well (there isn't that many wires in the system to start with - 18 would sound like most of them to me) - Have you swapped the engine complete with the loom, or removed your engine and done repairs to it?