On my 2005 ford f-150 lariat the lights go crazy. When parking/running lights are on turn signals flash fast but when u turn on one side both sides flash along with licences plate lights flash also. Reverse lights very dimb if even on. If just turn signals are on they seem ok unless u hit brakes then get slow. I checked the ground in rear of truck and ground in drivers kick panel both good, check connections in rear also again ok, also changed multifunction switch again no change, also all bulbs are good and fuses are good. Have I over looked something or am I missing something not sure what to try next

SOURCE: front driver side turn signal light doesn't flash

replace flasher......usually located in fuse block area...listen in this area....select passenger side ...then select driver side...you can hear flasher clicking...you have seperate flashers for each...FLASHERS are small cubes plugged into fuse block....probable bad driverside flasher

SOURCE: Both rear turn signal lights flash

Bad Ground!

SOURCE: 1997 GMC Sierra p/u. Brake light & blinker out. Lamp & fuse ok.

you probably got the wrong bulb
those are usualy a different number higher wattage, they look exactly like an 1127 but are a 2027 or even a 3027 check the bulb base it has the number printed on it

SOURCE: 99 Chevy Tahoe... Rear turn signals, brake lights, and hazards

I had this problem, and to be honest, it happened to the left side about a week later...it's the board that the bulbs plug into...it's a very common problem with this model. So popular that you can normally get the socket board off the shelf at a parts store! it's extremely simple to replace, and I replaced all the bulbs at the same time!