Troubleshooting Turn Signal Problems on a 1985 Ford F150

by John Walker
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turn signal image by Rob Hill from

The 1985 Ford F150 followed a similar setup to all Ford trucks and SUVs with regard to the turn signal. The signal routes through the ignition switch to the turn signal relay. The relay interrupts the signal before going to the light, allowing the light to flash on and off. Problems with any aspect of the system will cause the lights to not activate, or remain lit without flashing off. Determining the cause takes about 10 minutes.

Step 1

Start the vehicle and activate the hazard lights. The hazard relay is separate from that of the turn signal. If all lights flash properly, the problem is with the turn signal relay or the switch. Activate the turn signals for the driver's and passenger's sides, and monitor the activity of the lights.

Step 2

Replace the bulb if the same-side light on the opposite end of the vehicle flashes wildly while the corresponding light does nothing. You might have two burned out bulbs on one side, so check both.

Step 3

Replace the fuse if nothing happens at all with the turn signals but the hazard lights operated properly. The fuse panel is located beneath the dash at the access panel to the left of the steering column. Check the fuses for both the flashers and the turn signals. A diagram is printed on the cover to the fuse panel showing the locations of both. Needle-nose pliers make pulling the fuse easy.

Step 4

Replace the turn signal relay if the flashers worked but none of the turn signals activated, or all of the lights activated without turning off. The relay is on top of the fuse panel. It is a cylindrical plug in the lower corner of the fuse panel. It pulls straight out.

Step 5

Trace the wiring to the light fixtures. The majority of the wiring is hidden, so look at the connections to the bulbs. The chance of a problem with the wiring is very slim. Replace the plugs if there are major signs of rust or corrosion, and you are familiar with the process of splicing wires. Otherwise, you should have a professional replace the damaged wires.

Step 6

Take the vehicle to a professional to have the switch replaced if the fuse, bulbs, connections and relay are all operating properly.

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