Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

1990 Ford F150, turn signal wont work while braking

Our truck, a 1990 Ford F150 crew cab, has a problem with the turn signals, when we brake. The turn signal blinks on the dash board as normal until you press on the brake pedal. The same thing happens with the hazard lights. I have check the fuses under the dash board and they all appear to be ok. What is causing this malfunction and how do I fix it?

It’s probably one of the two suggestions below.

  1. The multi-function switch. One of the contact sets is stuck together. You’ll have to replace it.
  2. Alternately - If you have added a trailer wiring connector, it might be wired wrong and causing this problem.

That is kind of strange alright. Along with Tardis’s advice check the power gertting to the flasher unit with the brakes applied and make sure that is ok. Replacing the flasher unit may be necessary also.

Check the tail light ground connection.

As stated above, check the ground at the tail lamps. A bad ground will do exactly the same.

Also bear in mind, the cruise control in the multi-function switch may have a fault concerning your problem as the cruise control and the brakes also work in conjunction.