krismasmilaa

so i did a search on multiple forums and none of them have been much of a help to me. so let me first start by stating my problem, stating my attempt to resolve this problem, and requesting feedback or advice or even assistance from you guys

club s12 is a fairly old forum, i would post it there but the goddamn website wont send me an activation link so i came here as a last resort

My Problem:
So i have a 1985 200sx s12. it has a digital dashboard (as stated in the title) that literally has a mind of its own. nothing works correctly but the speedo. HOWEVER , i've traced down the problem of the fuel level, oil pressure, battery voltage, and coolant temp gauge to the sensors themselves; probably not making complete contact or so. So what is my problem? I want the tach to work at least so i can adjust my idle properly and fix my ignition timing but i CANT GET IT TO WORK.

What have i done to reslove this issue?
So for the tach, light stay on: The redline, the light at 0 rpm, and the light at 3000 rpm. Typically in a old ass 32 year old car, you would assume that the solder joints have gone out or broken. This was my first suspicion. When i pulled the cluster i, in fact, did find broken solder joints here and there. i reconditioned and re soldered almost all the joints of the control module and the power module of the cluster, however this didnt solve my tach problem. I tested the display of the digi dash via the method stated in the OEM FSM and all the lights of the tach do work. So i figured, maybe the previous owner didnt wire the tach correctly. Essentially, you should be able to hard wire a tachometer straight to the negative post of an ignition coil no? so i tried that, and still no go; those three lights are still on. I cut both wires that read "Tach signal" on the FSM and still nothing changed. now i would just try and hook it up to the positive post of the ignition coil, but according to the FSM, the one that goes to the coil has a negative polarity.

So what am i asking of you guys?
- should i give up and go aftermarket tach? (which i do not want to do cause it will look JANK AS FUCK)
- should i try and source out an analog cluster?
- are there any other options im ruling out ???