Panic Lamp

Many people worry about the Check Engine light, often calling it the Check Wallet light and maybe so but that light isn't the one that should scare you. The one light that should scare you every time it is on when it should not be is the brake light. The brake warning light being on could mean your death is immanent. You should never drive any car with the brake light on.

This light should operate under exactly three conditions on most cars. Manual transmission Fiero has a 4^th condition that will activate the light. This includes most cars with ABS. (Note that some ABS problems may trip both the ABS and Brake lights.)

The ignition key is in the lamptest/start position.
There is a major hydraulic problem in the system.
You activated the emergency brake.
You pressed the trunk release switch on a manual transmission Fiero.

This ignores electrical defects in the lamp circuit for a reason... While possible, this is the absolute last thing you should look for. You need to eliminate all the normal causes before looking for a short. If you have eliminated all the other possible causes, look at the switches and the wires near them.

Common electrical problems:

The wire to the emergency brake switch on many vehicles can get against the mechanism and rub thru.
The switch on the emergency brake or combination valve can break and stay on.
The switch on the combination valve can fail to turn on. This could be the result of broken switch or a bad combination valve. (Bad combination valves are often the result of bad fluid and the corrosion that comes with it.)

Hydraulic Failure

First read the Combination Valve. That article covers map of parts and how it works.

To help isolate this, find the electrical connector on the combination valve or master cylinder and unplug it. If the brake light goes off, there is some sort of hydraulic problem.

Obviously a leak in the system is a bad thing. If you can't find a leak then the master cylinder is your likely problem. The cup seals on the MC pistons can fail and cause pressure loss in one or both circuits and you won't loose any fluid from the system.

Pseudo Hydraulic Failure

Before you just assume that a non-leaking system has a bad MC, check the rear brakes.

The rear brakes on Fiero and other vehicles can cause what looks like a hydraulic failure to the system. This is the result of extreme pad clearance that allows you to squeeze the MC dry on the rear circuit. In some cases the mechanical emergency brake system can fail suddenly and produce the same effects as a fluid problem. This can happen with all of the emergency brake systems on the road but some, like Fiero, suffer hand brake problems with alarming frequency.

Emergency Brake

Obviously the light should be on when the emergency brake is active and the key is on. The problem is when it won't turn off after releasing the brake. If the emergency brake is not fully released you could fry off the pads/shoes really fast and even start a fire. Problems with the emergency brake system can also cause low pedal problems that are as bad as hydraulic failure.

In Fiero and some other cars... Many people think the brake handle activates the brake light but it doesn't. The ratchet that the handle operates to move the cables trips it. The two items are separate parts of the system. While the handle does pull the ratchet when you apply the brakes, it doesn't push it all the way back to rest when you let them off. Part of that job is left to the cable return springs at the calipers. If the cables don't pull the ratchet all the way to rest when it is released, the light will stay on. (Which is exactly what you want with this type handle mechanism.)

When the light won't turn off after using the hand brake try reaching under the car and pulling on the cable from the handle. If that shuts off the light then you can eliminate any problem at the handle. Depending on just how far from rest the ratchet is... You may need to have someone pull the cable while you release the handle.

If you do find problems in the emergency brake system, you need to go thru the whole rear brake system. Problems with the cables or calipers need to be fixed or the performance of the whole system and your stopping distance will suffer greatly.

Trunk Release

The Fiero trunk release option is wired to the hand brake switch on manual transmission vehicles. It is "normal" for the brake light to trigger and the gauges to move when the trunk switch is depressed under certain conditions. Normal but it is really a minor wiring error at the factory. (Much like the temperature gauge problem many Fiero owners are aware of.)

There is an easy fix for this. Install a LED 194 lamp in place of the incandescent warning lamp. Because LEDs are diodes and only pass power in one direction, this will break the sneak path that is created thru the gauges. Note that the LED lamps only work properly when installed in one direction. The LED should activate with the key on and the hand brake pulled. If it doesn't then you installed the indicator backwards and will need to take it out and rotate the socket 180°.