the little door switches are probably dirty, a little electrical cleaner spray(radio shack) on them may work... also...everyone should have a manual for their vehicle, and the local library should have a professional shop manual available, to make copies of, in the Reference section...good luck:)
Edit:
internet search reveals there may be an issue with the Lighting Control module.
Loose fuel cap. Try tightening the cap a little more the next time the light comes on. Happens to my wife all the time. What an interesting response! I have a 92 GM LS and it has 'suffered' from having the 'check engine' light appearing at random intervals for years......Ford checked it out when it was in the USA and we have run it here in the UK for 2 years and it runs beautifully - BUT, now and then, the 'check engine ' light appears...even after it has been serviced!! I'm tempted to get the bulb taken out :-)))
1988 Grand Marquis hubcaps have a lock on them. You'll need to buy it. The center panel (with the mercury logo) comes out and you'll see a little opening that is flower shaped. That needs to turn to release the hubcap from the lugnuts.
Check the brake light switch. It is defective or out of adjustment.
toyota estima/lucia have a common fault with the waste-gate actuator playing up.
The word mercury comes from the Roman god of speed.
It's a safety feature that comes with the car. There's a way to turn it off, but you'd need the owners manual to do it.
The origin of Mercury comes from the Greek gods named Apollo & Hermes.
Venus
Have you checked to see if the elect. fan comes on ?
Transition metals Zinc group or group 12 Zinc, Cadmium, Mercury
Mercury was named by astronomers in 4th century BCE. The name comes from the Roman god Mercury, who was the messenger god and the fastest of the gods.
Mercury