how to turn of maintanaance light of on 02 mercury cougar

What maintenance light?Check engine light? 2002 mercury cougar does not have maintenance light.

Well if it really does not need maintainance , - it can be ''turned off'' by disconnecting battery for abouit 10=20 seconds, then re-connecting!

But be aware though -- that if u have one of those fancy ''anti theft'' burglar alarm systems, - u better make sure u know the ''codes'' & procedures to get vehicle '' back on track'' as to radio & ignition systems! Because these systems may think that u r trying to ''steal ur car''! If it does then it shuts everything down! If u have the owners manual it will probably give u the information, -- if not u will have to call the dealer,and find out what to do!

Anyway after diconnecting batery, - it ''looses it is memory- & starts all over from ''0'' again! If the service light remmains on, -- it means that something is wrong, & u better take it & find out what it is!

l dont think the overhead lights (sport package only, right beside the sunroof controls) were available on that year. The only way to get a Maint light was on the overheads.

The CEL light can be turned off by diconnecting the battery--this will not cause any issues with ur security system.
Disconnect for a bit, reconnect & the light should go. If u have an actual problem the light will come on shortly & u need to have it checked out.

Before u disconnect the battery u should go ahead & get the code read though-Autozone will do it for free.

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If u do have an overhead maint light then the easiest thing to do is just run by Mercury or another shop & just ask them to show u how to kill it.