My 1990 toyota corolla tail lights and dash lights stopped working after i hooked up a stereo and sub and amp system...i checked the fuse and its good..i cant find any wiring problems..help? anybody?

tail Fuse 18--15 amp, interior fuse box.
Not only check the fuse, check the fuse circuit for voltage, hot all the time, use a test light to check for voltage.
There is another fuse and fusible link involved. First, check for voltage on the tail fuse.
Some people want to know exactly what the problem is w/o any testing, usually, I can't do that.

I found this useful diagram at troubleshoot vehicle.com. It answers your question. Fuse box is located below steering column.
Driver Side Fuse Panel
(1993-1996 Toyota Corolla) December 21, 2013 Updated: December 21, 2013 Written by: Abraham Torres-Arredondo In the table below you'll find the fuse location and description of the fuses of the driver side under-dash fuse box on 1.6L and 1.8L 1993-1996 Toyota Corolla.
The fuse box is located on the driver side of the dash, below the steering column.
1993-1996 Toyota Corolla Driver Side Fuse Box Fuse Fuse Name Amps 1 Cigarette Lighter, Digital Clock, A/C System, A/T Shift Lock, Alarm, SRS Airbags 20 2 Tail, Parking & License Lights, Instrument Panel and Daytime Running Lights 15 3 Fuel Injection, Cooling Fans, Battery Discharge Light 10 4 Cruise Control System, Daytime Running Lights 10 5 Fuel Injection System 7.5 6 Stop Lights, Cruise Control, Shift Lock System, Anti-Lock Brake (ABS) System 15 7 Turn Signals, Emergency Flashers 10 8 Starting System, Anti-Lock Brake (ABS) System, Shift Lock System 15 9 Gauges, Reminder Lights, Back-up Lights, A/C System, Daytime Running Lights 10 10 Front and Rear Wiper/Washer System 20

change your dimmer light switch and check the "tail" fuse

the tail light issue could be just bad bulbs, check them with a meter ,, also, check the sockets for power to each contact point,, normally if the brake lights and flashers are working, the tail lights should too,, as far as the dash lights have you installed an after market stereo? If so a common problem is a wrong wire got grounded,The harness from the car to the factory radio has a wire for the dash lights that shows up as ground with the light off. When the lights are on the wire is 12V+. Check to see if you connected the ground from the new stereo to this wire. The radio will work perfect but everytime you turn thr park light on the fuse will blow...and the radio will continue to work. There should be a ground wire in the harness as well, ensure you connect the ground from the new stereo to this wire. there is a 15 amp fuse that blows, check them with a meter rather than by sight

Its the brake pedal switch under the dash. My 1989 did the same thing.

I had the same issues. Dash dead, tail lights dead. Fuses were fine, Dimmer relay was fine...So I got to the Tail Light Relay.

Removed the glove box, one screw on the right. Reach up (above the space where the glove box 'area' would be and there are 3 or 4 relays all sitting on top of a junction box. All of them were loose. I pushed them in...and voila! I was getting scared after the obvious.

Toyota is not consistent.
Check then all.
If any fuse has power on one side, and none on the other, then that fuse is bad.
It could easily be that both bulbs went about the same time. It happens frequently.

check the switch on the break pedal,replace as necessary.

check the fuse box for blown fuze

I would look for a wiring short in the trunk at the taillamp area, or, inspect the sockets for the taillamp bulbs for corrosion. In any case, you have a short circuit in the trunk area, also check the wire that comes from the body & goes up the trunk hinge on the driver side; that wire may be chafed, and it may be shorting out. Hope this helps; please get back to me if you need any further assistance.