Tachometer doesn't work

[Ryan Wright]

Need some help with my tachometer. As the story goes, it quit working
so the previous owner had a brand new one put in but it didn't solve
the problem. Sure enough, I have a brand new tach in my dash with all
zeros on the hour meter that doesn't work.

I'd like to fix this. I think the tach is a rather important piece of
equipment. :-)

Any advice? I have no idea where to start, other than finding the
sending unit or engine connection (where?) and testing (how?) or
replacing it, and/or tracing the wires between it and the tach.

One note: Three of the wires going to the tach - two white (on the
same terminal) and one grey - all have had their insulation MELTED off
from where they connect to the tach, back several inches. This scares
me. Thankfully, the damage does not extend into the wiring harness;
just before the wires enter the bundle, they're fine, and everything
else under the dash is pristine. I traced the bundle in question
several feet into the dash and the tach wires are intact throughout
there. So, not sure what the deal is or how this happened. Sure looks
like overloaded wire damage to me but usually that extends throughout
the wire and damages other wires in the vicinity; this is not the case
here.

Thank you for any clues you can offer me.

-Ryan
'86 PT-40 8V92
Tri-Cities, WA