Alright boys, I've got some interesting news for you.
Yesterday I pulled and cleaned the main engine ground strap, and had great success with voltage and cylinder harmony.
So today I figured why not go one farther and replace the ground strap altogether?
I went to a local car audio shop and asked them to make me a ground strap out of their heaviest gauge wire with the terminals soldered on and then crimped.
So, half an hour and twenty bucks later, I had myself a very nice ground strap covered in heat shrink.
So I get it installed, fire up the car, lo and behold, my tachometer works! It kept on working for the rest of day without fail, steady as can be.
I'm very excited about this because I was not looking forward to pulling the pod to fix the connections.
So then I decided to change the battery ground strap, too. I didn't see any appreciable improvement except for a slight climb in overall voltage on the gauge.
Oh yeah, the car now starts on the very first try instead of on the second or third try.
I read out both old cables with my ohmmeter, and they both showed perfect continuity. But just because a little ol' nine volts can find it's way through a cable doesn't mean that cable can carry a heavy load.
The main engine ground hangs VERY close to the exhaust down-pipe on the passenger side. I'm convinced this extreme heat is what ruined the cable over time. I don't expect my new cable to last very long, either. It's not made for this application, but served very well to uncover that big current limiter.
Pics:
