Expert: Brad Sears - 10/14/2010

Question
QUESTION: I have a 1983 Mustang and the front turn signal is not working correctly.  The bulb (1157 (double filament)) was burned out so I replaced it.  Now the bulb stays lit up (both filaments (one side much brighter than the other)) when the lights are on and it does not blink.  The indicator on the dash blinks correctly and the rear bulb blinks correctly.  Please help.

ANSWER: This sounds very much like a defective ground. Follow the ground wire from the socket to its attachment point on the front fender inner panel. Clean the connection and see if it works. If it still does not get back to me and we will go from there.
Brad

---------- FOLLOW-UP ----------

QUESTION: Grounds were all good.  I check the wires (3 (+,+, & -)) and found that one + was constant (running light) and the other + was relaying power on and off properly....hmmmmm.  I then checked the soket carefully > OK.  I then look at the bulb...it was in opposite to how it is supposed to be.  I thought those bulbs (1157) were designed to only be installed one-way.  However, I believe the socket is worn just enough to allow the bulb to be installed opposite to how it should be.  Oh well...the grounds all got redone.

Answer
The 1157 bulb does have offset pins that means that it should only go in one way. But is some one in the past forced a bulb in the wrong way then it might go in backwards. If this is the case the bulb itself may not be making a good contact to the socket and looking for ground in the running/parking light circuit. Is it working now? If not let me know. It is possible that you might have a defect in the directional switch assembly but that is a story for another day.