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Jim Grant's Tech Tips
Ford
F-150, No Brake Lights
Q: I have a Ford F150 p/u truck. The brake lights will not work. I’ve
replaced the switch, bulbs, cleaned all grounds and sockets!!! I have
rear lights, but cannot get brake lights to work. This is not the 1st
Ford truck I've had this problem on!! Got a match??
A: Save
the pyrotechnic display for later. I have to ask, did you check the fuse?
Did you use a test light or just look at it? One of the more effective
tools in diagnosing an electrical problem like yours is a test light.
The test light allows you to prove if electrical power is present in the
circuit before replacing parts. With a test light, start at the fuse,
then move to the stop light switch. The stop light switch should have
electrical power to one terminal of the connector at all times. If not
check wiring back to the fuse. When you push on the brake pedal a second
and third terminal (if equipped with a third brake light) will have electrical
power. You didn’t provide the year of the vehicle, so I had no way of
reasonably checking a wiring schematic so it makes it a little difficult
to be sure but here we go. Many vehicle’s brake light circuits share the
same wire as the turn signal. If this is true on your vehicle, turn the
directional signals on. If they work on both sides on the rear of the
vehicle then the wiring and bulbs to the back are good. If the stop light
switch is good and the wiring to the rear is good then you likely have
a bad directional switch. Why? because the brake light circuit travels
through the turn signal switch. Following a diagnostic path to prove a
problem will save you vs just plugging in parts.
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