Dash gagues not working

I didn't see an s15 in that model year, in my database?
If the speedometer works but the tach doesn't, I think something is wrong with instrument cluster?
GM has had a problem with fuel gage sending units. The sending units are not hard wired to instrument cluster, they send signal to pcm, the pcm sends serial data to instrument cluster, telling the cluster the gage settings.
It may be possible to use different size resistors in place of the fuel level sending unit, to see if fuel gage reacts properly to different resistors, if the gage reacts properly, then I think the problem is the fuel gage sending unit.

Hi, this is a pretty common problem on these Silverado instrument clusters. We can definitely help you out with that. Click here to learn more about these Silverado instrument cluster problems: Dr Speedometer Instrument Cluster Repair Speedometer Repair Guage...

The fuel level gage sending unit is defective, very common problem. The sending unit comes with a new fuel pump and is referred to as a module, also make darn sure you replace the fuel pump connector at the fuel tank, solder and shrink tube the new connector on, DO NOT USE CRIMP CONNECTORS.

check fuse instrument panel or gage /cluster

I'd wager that the fuse that controls the gauges is shot, or one of the internal connectors got unplugged (Fuse sounds more likely). Radio, Lights, and Turn Lamps are usually on seperate circuits.

something with your cars ecu ( computer) or possibly your battery. Make sure it is grounded and hooked up properly.

sounds like a fuse

Have the computer checked

the problem might be in the ignition switch(not where the key goes) but what the key switch is connected to. just try this first, when the gagues stop working, hit the steering column behind the key switch and if the gagues start working then replace the ignition switch

I'm going to assume you checked the fuses, and say that the display panel will have to be replaced. On these the display is all one piece, and when one gage goes out it effects the whole thing. Some of these display panels had in line fuses on the inside circuitry, so you may be able to pull the display and change the fuse. Others were built as a sealed unit and cannot be taken apart.