Here are the complete 1978 Toyota Pickup truck wiring diagrams in PDF form. You'll have to click on the link shown to download the file & save it to your computer to view the diagrams, but at least you'll have them on file.
These diagrams should also cover pickup model years from 1972 to 1978. I do not know what year Toyota started with the "emissions computer" on these trucks, so trucks older than 1978 may or may not have one.
I was informed that these are original Toyota diagrams published by Mitchell manuals. I've been over them a lot with my truck and have found no problems or errors in them; all wire color designations & wire connections have been correct.

I have also included the Toyota wire color codes below for reference.

 

Thank you. I was looking for these diagrams, but recently discovered that I couldn't open them. In general, I use an online editor https://pdfguru.com/forms/da-5960-form to fill out DA Form 5960 online, and I tried converting the file to another format. It worked, and I was able to open it, so if anyone else encounters similar problems, this might help. I think the issue was with my PC.