Turn signal flashes fast on one side only

We checked bulbs and even replaced them, but still doing the same thing.

Are both front and rear flashing fast on that side?

Hi, you didn't mention what year the M.G.M was so I can only give you general information. When asking a question always give as much info as possible about the vehicle in question like make, model, year, etc. anything that pertains to the problem. All the bulbs are basically on one main circuit line but pair off to each as is the flasher that controls them. If one bulb is burned out or corroded or just bad, the flasher will still open and close but now faster because of less resistance on that side. . Recheck ALL the bulbs even on the opposite side of the car too. If it's flashing fast on the passenger side, you got a burned out bulb or a bad connection somewhere but not necessarily on that particular side of the car and vise-virsa. Check both sides as that flasher under the dash controls the turn signals on both sides of the car. Does the car have cornering lights? That's a big white light on the front fenders that comes on and stays on while the turn signal is on as you go around the corner thus the name.. If that's burned out there's your problem. It's usually down low but again I don't know where exactly on your Grand Marquis as you didn't give the year of the car and different years are different locations. . Also check those little bulbs in the parking lights. My Crown Victoria (virtually the same as a Grand Marquis) has numerous little bulbs on the front corners of the car and you just might be missing checking them all. Sometimes you didn't even know one was there. They don't all flash but are on the same main circuit. Best to check for a burned out bulb at night in your driveway or inside the garage where it's real dark. You might notice something you overlooked in the daylight. Turn on your 4-way flasher to check all the bulbs at the same time. Wiggle bulbs and check for corrosion with each by pulling bulb and reinstalling then wiggling them to see if there's a change in brightness that you wouldn't see or notice during the day. If all the bulbs light up and are good then it's got to be a bad ground somewhere and unfortunately that could take a long time to find but again, just recheck all your bulbs and their connections. It might take awhile but you will find it eventually. After cleaning and checking all the connections, spray some dielectric compound (comes in a spray can at the autoparts store) into all the sockets and connections. This stuff stops corrosion from starting and stops it from coming back too. .Sorry I couldn't be more help.. Good Luck, Kenny/MrBlueOval

I don't need many details :-) That is a common problem. I had two 2000 Grand Marquis, and they both had this problem. There is a 'bug' in the electronic light control module. You need to find a replacement box, and this will cure the pain. Worked for me - both times...

it is a2007 im looking for the flasher

Something similar happened to me on a MGM 2006, the signal lights would turn on and it seemed the bulbs were working correctly, both turn signals were flashing fast, so I started thinking of the relay since both sides were doing the same, after some Internet search and manual reading found a video on youtube from an expert, took the back lights off and found one of the bulbs on each side was not turning on, it has two on each side, both light bulbs are good, brand new, but incorrect number, it takes 3157 and it had 4157 (form the manual), replaced the incorrect bulbs and turn signal speed was fixed, turns out whoever replaced them, changed one on each side with the incorrect number, which lead me to believe it was a problem with the flasher or circuit somewhere else. here's the video link: https://www.youtube.com/watch?v=t5qE5LioK1s

I have a 2000 Mercury Grand Marquis doing the same thing. MercLuver, or anyone else who can answer definitively, is the electronic light control module the only thing that can cause this problem. It's not cheap and I don't want to waste money on it if that's not the problem. Thanks.

I have a 2003 MGM I just bought. Had the same issue. I replaced all the turn signal bulbs. They were all the original factory bulbs still in the car, never replaced. Still all seemed to work. Once I replaced them, the turn signals worked normally. Spent about 24$ with tax. Do this first.

Mercury Marquis 2006. Both the light rear bulbs are type 3157K, and BOTH are both tail light and Blinker/Brake lights. If your lights are blinking too fast (you can test by activating the emergency flasher) check that you have blinking on all four corners. If one of the front is not blinking, replace it. If they are all blinking too fast and the fronts are good, remove BOTH rear taillight assemblies (3 nuts) under the carpeting behind each light in the trunk, then remove each light socket on the light assembly by gently turning it counter clockwise about 1/4 of a turn. You will find that one of the exposed bulbs is NOT BLINKING. Replace this bulb with a new 3157 K. DO NOT TOUCH THE BULB WITH YOUR FINGERS. USE A NAPKIN OR PAPER TOWEL. This should apply to all 2003-2010 models. Remount the bulbs, turn off your emergency blinkers, and with the ignition on, test left and right blinkers which should now be normal at approximately one Bink per second.