Dash / instrument warning lightsThe electrical fault light.This warning light is different in every car but normally it looks like a picture of a battery, similar to the picture on the left here. You'll see it come on and go off when you start your engine as part of the car's self-test, but if this light comes on and stays on, it means the electrical charging system is no longer working properly. Think of it like a cellphone battery. If the cellphone is plugged into the charger, you can use it indefinitely, but when you disconnect it from the charger, there's a limited amount of time before your battery runs out. It's exactly the same in your car, only bigger. Every car has an alternator - the charger - and a 12v battery used to supply power to the electrical system. If the alternator becomes faulty or the drive belt to it snaps, then it will not be able to do its job. The longer you drive, the more your car will use up the remaining juice in the battery and eventually the engine will die. This almost always requires a new or refurbished alternator.
Brake warning light 1Most cars nowadays have a brake warning light on the dash. Its purpose is to alert you that something is wrong in the braking system somewhere. If it comes on, check your owner's manual to find out its meaning. Unlike the single-purpose ABS warning light, the brake warning light doesn't have a standard meaning; it could be used for multiple purposes. For example, the same light may be used to show that the hand brake (parking brake for the Americans amongst you) is on. If that's the case and you're driving, you ought to have noticed the smell of burning brake dust by now. The light can also indicate that the fluid in the master cylinder is low. Each manufacturer has a different use and standard for this light. Which is nice. Because it would be such a drag if the same indicator meant the same thing in every vehicle.
Brake warning light 2If you've got an ABS-equipped car, you also have a second light - the ABS light. If it comes on, get it seen to as soon as possible. It means the ABS computer has diagnosed that something is amiss in the system. It could be something as simple as dirt in one of the sensors, or something as costly as an entire ABS unit replacement. Either way, if that light is on, then you, my friend, have got 1970's brakes. It's important to note that this light normally comes on when you start the car and then switches off a few seconds later. If it stays on, blinks, throbs, flashes or in any other way draws your attention to itself, take note. It's not doing it just to please itself.
Coolant warning lightThis is normally the coolant level warning light. If this comes on it means that the level of coolant in your radiator is low and needs topping up. DO NOT OPEN THE RADIATOR CAP WHEN THE ENGINE IS HOT! The coolant system is pressurised and it could easily release pressure and spray you with boiling coolant. Do it when the engine is cold. Top up the system with either a pre-mixed coolant bought from a shop, or with distilled water. Don't use tap water - the mineral deposits in it boil out in the cooling system and calcium gets depositted around the inside of the radiator making it less efficient (which will eventually cause it to fail). It's always best to use pre-mixed coolant, or to mix your own rather than using neat water. The coolant mixture behaves as an antifreeze in winter as well as a corrosion-inhibitor to stop your engine rusting from the inside out.
Oil warning lightTypically this light will come on if your oil pressure is too low. Low oil pressure is serious and if you continue to drive with this light on, eventually your engine will die. Low oil pressure can be caused by a failed oil pump, a blocked oil filter or strainer in the sump, or by low oil levels.
