Have you tried turning the knob that turns your head lamps on? Sometimes that will turn your interior lights back on. Also, you might check the fuse box that is located under the dash on the drivers side, there may be a fuse blown.
Try the lightbulb it self, corrosion on the contacts
Fuse connections. The connectors for the dome light in the fuse panel get loose, you can try and bend them back with a small screwdriver to make the connection again.
Check the circuitry to the backup lights. The same fused circuit is probably used for both brake lights and backup lights. As you go past Reverse, the backup light probably is turned on briefly, causing the fuse to blow. It's just a thought, but I'd think it worth checking.
I think it is cause its true, she dont like the light
It can be interferance caused by Fluorescent lights, Transformers, (such as battery chargers) switchless lights, you name it. Anything that plugs into electric current in your home can in one form or another. In your quest to find the problem, you will often overlook what the actual problem is.
The primary cause for jerking on a 99 Mercury Cougar is the engine not getting enough fuel. This can be a sign of a clogged fuel filter, bad fuel pump, or clogged fuel injectors.
you dont need to cause it has a factory tachometer
There probably is only one cause for your interior lights to go on when you apply the brakes. There probably are brake light wires and interior wires that have warned together.
probably the fuel pump?
I had the same problem in my 1999 Mercury Cougar, I replaced the flasher located in the blinker assembly. It was very simple to do. Flasher cost about $10
Try your voltage regulator
The most likely cause is a dirty fuel filter that starves the engine.
my son bought a 1996 cougar that felt like the transmition was slipping and we had the transmission flushed and it fixed it.
probably the fuse is blown.
the ignition timing set wronge. BAd accelerator pump in the carburetor
it is in the manual says when this happens it is 02 sensor and if it is flashing you have a miss in your engine which can cause damage.
check the recalls for the 99 mercury cougar!! it includes a recall on the throttle cable...