1990 blazer electronic dash not working

Sounds like the body control module has gone bad. It has a relay that caries considerable current to all of these accesories and wears out.
It can also be a solder joint on the circuit board where this relay mounts.
Hope this helps, Robert

Dash board or gages

These lights for the dash are controlled by a rheostat instrument control dimmer switch next to the main light switch for the headlights, it is either turned off (have seen this dozens of times) or it is defective. Below is a picture of the switch assembly I speak of. The thumb wheel next to the knob is the dimmer control.

Behind of fuse box( located by emergency brake pedal) is a module, this one controls all gauges

check the fuses under the hood in the power distribution box. might be one blown there as well

this vehicle has an electronic speed sensor located on the trans i do believe but im pretty sure this is your problem change it and your cured

I know your fuses look good but try replacing the fuse with a new one.

My gas guage, speed odometer and tempiture does not work
The speed odometre is reading 9999999 what should i do

Speed sensor has failed.

It is basically a magnet sensor that reads the RPMs of the tranny.

It is screwed into the side of the transmission.

Do you have an aftermarket alarm installed, or remote start?
Sometimes those wires can be damaged if not installed properly.

It is $33.00 at autozone.
Part #SU1090



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Remove the instrument panel form the dash. Pull the back off and resolder resistor R13 on the back circuit board. This is a fairly delicate job and requires a fine pointed soldering iron. This fixed the Tach, Odometer readout, and fuel guage but not the speedometer in my 85 900 s.

Any ideas on the speedometer?