I have my 98 oldsmobile lss supercharged and recently a buddy of mine wired up a new head unit. About 4 days later my alternator went. I replaced it but during the process, my gauges were going wild (I assume from the loss in voltage). I fixed the alternator but a new problem arose, my temp gauge is always reading 0. My gear shift light is out (not on the dash). My outside temperature is flashing on and off. Something is fried but I'm not sure what it could be. My scan tool reads the temp so I know my temp sensor is fine and the gauge is actually getting power since if I manually move it, it tries to drop it back down to 0. I brought it to a mechanic and they said they think it'* the instrument cluster. Before I get into this rabbit hole of crap I'm looking for some suggestions. Any idea what it could be? Also I'm looking for the instrument cluster pinout - if possible I'd love to just wire an aftermarket temp gauge if that one really is fried for whatever reason. I know it'* a dark green and 2 pink wires but I'm not sure about the pins and for which cluster plug it is.

I'd start by removing the head unit that was installed right before all of this happened, then look at all of the wiring for bare spots and shorts to ground.

What he says'

the head units been out for awhile now, it still happens. All the wires were soldered on and then we put heat shrink over them so I'm not sure it would be that. I gave them all a little tug to make sure the solders were good and they all seemed sturdy.

Okay so here'* what I see:

1. "I have my 98 oldsmobile lss supercharged"
2. "recently a buddy of mine wired up a new head unit"
3. "4 days later my alternator went"
4. "I replaced it but during the process, my gauges were going wild (I assume from the loss in voltage)"
5. "new problem arose, my temp gauge is always reading 0. My gear shift light is out (not on the dash). My outside temperature is flashing on and off."
6. "Any idea what it could be?"

So . . . it was fine, then a buddy wired stuff, then it was broken, and now it is still broken. You need to find the short that caused the damage. If you fix any of the other issues they could get broken again by whatever this problem is.

Has every single modification been removed? . . . and now nothing looks changed at all?

It'* not just an analog connection to the sensor. It'* going to the BCM. If you want to wire in an aftermarket gauge, you'll need to run wires from a sensor to the gauge.

Do you need any factory info? I have it.

So, I did actually check all the wiring and it all looked proper and good. I traced every wire, the ground the ignition everything was good. The shop I took it to said they looked it over and it looked good as well. My theory is the alternator blowing was coincidence and mightve sent a surge or something that fried the gauge inside the cluster. I don’t feel like getting a whole new cluster so I’ll probably just get a new gauge + separate sensor altogether. I did end up unplugging the head unit and The temp gauge is still dead.

I haven't had a chance to look these over but here'* wiring of the cluster.

It fixed itself yesterday on my drive home. That means nothing was fried, maybe a lose connection. I noticed my gear shift light (next to my shifter) came back on and was functional which it was not after this problem occurred. My traction control button also regained functionality. I am now in desperate need of a schematic that shows where at least one of these things goes. Since they all are clearly connected at one point or another I’m starting to think theres a lose connection somewhere. If anyone can help with that I’d appreciate it so much … 1998 Oldsmobile LSS L67 SC

I don't know why you didn't just update your original post. I'm lost.