Check the fuse, check the bulbs and check the brake light switch, in that order.
The head light switch is shorting out ,or a bad connection
Just a suggestion, check your trailer lights harness for corrosion. They were taking the dash lights down in my chevy.
Check fuse, check bulbs, check brake light switch, check wiring and then check signal switch, in that order.
If you have no dash lights at all on your 1989 S10 Blazer, a blown bulb can be the problem. You should also check the fuse.
change the headlight switch it controls the running lights....$15 at autozone
DOT 3 Brake Fluid
Brake light switch out of adjustment or defective
The alternator may be on it's way out.
If a 1991 Chevrolet S10 Blazer warning brake light always stays on, it could just be a malfunction of the light. To reset it, disconnect the battery for 10 minutes.
Check the fuse, then the bulbs, then the brake light switch.
The library should have a shop manual...