That wire is also grounded to the stud that is attached (welded)to the inside of the front bulkhead under the dash. About directly above the clutch pedal.
That one is really tough to get at unless you pull out the dash OR remove the speedometer. If you have a single pod dash, I would stay away from attempting that. A dual pod is POSSIBLE for human hands to get back there, but a single pod, well...it just ain't!
Everyone of these ground studs that I see has very heavy and obvious surface corrosion on it from "flash rust" which is what happens to steel based metals that are exposed to just the oxygen and the moisture normally in the atmosphere.
As a result, that ground just normally will "go away".
The blue wire in the harness, the one that looks like a strange circus color bright blue, is the sensor or if you will, trigger wire from the ignition. It just runs to the white plastic tach harness plug behind the gauge BUT the tach connection is just on a spade connector with the origianl Italian style "quick connect" jumper female plug.
They often wiggle themselves loose. I have even seen them break off of their mounting to the tach case.
There is also a wire in that mini-harness (pink?) that is the 12v power from the ignition switch.
Be advised that when these Pantera ignition switches "go", they sometimes are selective internally as to if they are going to supply current to every wire that is connected to them?
So besides the possibility that the tach itself actually died on you, which is probably the remotest possibility, you have to eliminate the other connections I just mentioned as the culprits.
Now there is also something else that you didn't mention, that could be a player in this as well. An MSD ignition.
If you should be so unfortunate to have one installed in the car, then it undoubtedly has an MSD tach adapter piggybacked along with it, and maybe an exorcist can help you with that?
They are subject to all kinds of connection issues. Whether it be from their own add on harnesses or loose or maybe better stated as "not tight enough" connections to this unilateral decision that they seem to make that lets screw with this guy now.
I've seen racers change them out three and four times a season. The brain just goes away. Where to? I don't know. Maybe to ACCELL?
That actually is quite simple to remedy though. You rip the entire MSD entourage out and install a Pantera Electronics Ignition.
Enlightenment sometimes comes hard? It surely does for me.
