I have a 1997 chevy blazer with check engine light on, speedometer and rpm not working and gas gage stays at 1/2 tank. First it was just the check engine light on. Got a tune-up, checked the computer on truck for problems, had wires traced for possible shorts. Check engine went off for couple hrs while mechanics checked out car. It came back on while I drove it home. I called mechanics and they don't know what the problem is. Since then, the speedometer, rpm, and gas guage stopped working. I changed out the fuses but the problems continue.

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.

The ABS light is on, because you have no speed signal. The transmission is not shifting for the same reason. The core of your problem is the speed signal. I would first check the speed sensor wires again. One of them may be broken. If not, then you may have popped the ECM (Vehicle Eletronic Control Module). Good luck.

Could be the sending unit in the tank, or the gauge on the dash. A mechanic would check the signal from the sending unit at the tank.

may be the air pump,having water in it .this does not mean that the pump it self is bad but a breather tube or something smaller.had same problem on 5spd saturn

Here's a link to the wiring diagram for the 1997 Chevy Blazer.

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.

you can get the required fuel pump for you car from the above link.you can also get proper details about the cost and the part from the above link before you order the fuel pump.http://www.autopartswarehouse.com/mmp/chevy~blazer~fuel_pump~parts.html check out this.keep updated for any further assistance. thanks.

This is a common problem with Malibu's. It is due to cheap metal in the fuel gage that corrodes. Chevrolet knows about this but they refuse to issue a fix. The check engine light staying on and the faulty fuel gage are related. This is a defect and they need to recall this part! Raise hell with the dealership!

check operation the throttle control motor or cable if used ( broken /missing return spring

Yes it is all one unit, and yes that is what the problem is. don't use aftermarket parts, use OEM, (Delco Remy) they are much better quality.