First of all if all your lights don't work then its your switch I was told on my 94 it was the switch when my tail lights wouldn't work but all my other lights did. if that's your case or vise versa then its a bad ground somewhere. If not there is some mounting hardware under the dash almost where your fuse box is.
On your 1989 MERCURY TOPAZ, the BACK-UP LIGHT SWITCH is: UNDER HOOD, DRIVER SIDE, LOWER ENGINE AREA, MOUNTED ON TOP OF TRANSMISSION
First what is wrong with you headlight switch on your 93 topaz.
You don't. The switch is all one , you will have to replace the entire switch.
Why ? Just replace it.
Is there a gauge panel dimmer wheel switch ? Try rotating it , it may be rotated all the way in one direction
Because your switch is bad, replace the light assembly
Its just a geuss. but on my 93 mercury topaz the head light switch alsoe controls the lights in side the care. If it's clicked all the way on that might be why.
This is usually cause by a stuck brake light switch on the brake pedal. Replace it.
Follow the positive cable wire from the battery and it will end up plugged right into the safety switch.
check your brake lights if they not worhing replace fuse or brake light switch
Get the alternator checked before your battery goes dead.
How do you replace a break light switch on 1995 Chevy Tahoe