I assume you are just fixing old wiring and not installing a new harness so......
I really don't know what you what to know and I don't understand why you are messing with silly pedal wiring and trailer wiring? REMOVE everything that is not original and use the diagram to wire/rewire the truck. We can't answer questions about unknown, very old, add on trailer brake wiring and etc. It's junk. Remove.
As far as the tach wiring. Do you actually have an optional stock tach? Post a link to the diagram you are using and I will help further.

What about this comment? seems you already cleaned it all out and were OK???????????? weeks ago??????

"Thanks for all the advice everyone. Believe I have all the extras out, Properly soldered and shrink wrapped the obvious bits together. Since it is all accessible the next step will be to inspect every wire for anything missed it nicked, check grounds, continuity check, and hit the power. Fingers crossed...
Once again, Thanks!"

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn