On an 87 F150 I am having brake light issues. I had been having problems with the signal lights so yesterday I starting troubleshooting. At first all rear lights worked great. Then I started up the truck and only the left side flasher and brake lights worked. A couple of days before that neither brake light or signal lights worked.

I have replaced the flasher and checked all of the bulbs and fuses.

What could be causing these problems? Any ideas?

 

Check the grounds and the contacts in the plug. Then go back and check your grounds. After you get all that done make sure you have a good ground. Ford always did have an issue with the taillights and bad grounds.

 

Stop light switch....located under the dash on the brake pedal assembly near the top. Its purpose is to turn on the brake lights when the pedal is depressed.

Should be a cheap switch and easy to replace.

 

True, I forgot about that, also check the plugs under the dash and make sure everything is tight together. I have seen them cause problems also.