03 F350 W/ no brake lights. Yesterday I was told my lights were not working. When I looked I noticed that both turn signals and hazards work but no brake lights. Trailer plug = same. Any idea this goes against everything I was ever taught.

 

Could it be something as simple as the brake light switch on the pedal?

Duncan

 

Do you have the adjustable petals?? I ahve seen posts about the switch on them going bad

 

My vote is the brake light SW because the pedals moved and partially disconnected it...I know it is a stretch....

 

Could it also be a fuse?

Does anyone know if the brake switch is a motion switch or pressure switch?

Just curious.

 

Brake lights and hazards are on a separate circuit and fuse from the turn signals. It is fuse #18 (20 Amp) in main junction box under dash. Check the fuse. If the fuse and bulbs are good then check the output side of the brake pedal switch for power. Pin #5 Light Green/Red wire is supply voltage to switch (should be at least 10v to ground), Pin #4 Light Green wire is wire from switch to stop lamps.
If there is power leaving the break pedal switch, check for power at the bulb sockets. If no power at the sockets then trace the wire to the light sockets looking for a break in the wire. It is a Light Green wire.
Since the hazards are working i would suspect the Brake Pedal Position switch as the most likely canidate.

Hope this helps

 

It is a pressure switch attached to the master cylinder pushrod at the brake pedal arm.

 

Probably should clarify my previous post, dry pressure switch that master cylinder pushrod moves. Not a wet pressure switch that the hydraulic fluid activates.

 

Power on both green leads w/ power on solid when applied. no power at socket on brakes or trailer plug. I also cant find any broken or damaged wires. Is there a module or diode that seperates turn, hazard, and brakes?

 

When the power leaves the Brake Pedal Position(BPP) switch on the Light Green (LG) wire pin 4, it is split in three directions;

1) It goes to the tralier brake control connector under the dash.
2) It goes to the high mounted stop lamp at the rear of the cab.
3) It goes to the "Multifunction Switch" in the steering column.

The LG wire enters the Multifunction Switch in the steering column at pin 1 of the connector C202a (10 Pin). There is also connector C202b (12 Pin) at the Multifunction Switch. Power comes out of C202b at the Multifunction Switch and is supplied to the right rear OG/LB (pin 8) and left rear LG/OG (pin 9) Park/Stop/Turn lamps, and the trailer tow relay turn signals in the Auxillary relay box under the hood.

The simple test at the multifunction switch is to disconnect C202a and while pressing on the brake pedal, measure the voltage at pin 1 LG to ground. If voltage is 10v or greater then the multifunction switch is bad. If less than 10v then there is a break in the LG circuit between BBP and Multifunction Switch.

Note: there is also a long multiple step component test of the Multifunction Switch jumping between both connectors C202a & C202b in different combinations. The multifunction switch plays a role in the turn signal, stop, park lamp, headlights, and winshield wiper operation. To access the Multifunction Switch in the steering column you must first remove the ignition switch lock cylinder, tilt wheel handle & shank, and the upper & lower steering column shrouds. Without a service manual in front of you it is difficult to explain the component test of the Multifunction Switch and the dissasembly of the steering column.

IMHO if i were you i would take my truck to the dealer and let them find the problem. It should be under warranty and i am guessing by the nature of the Multifunction Switch and its location that it is an expensive part to purchase and replace.

Hope this helps

 

Thanks for the info. I have driven 80,000 miles so my warranty is long gone.
I'll try to round up a manual. Thanks for your help