Hello,

I've looked for this problem and didn't see it anywhere so forgive me if this is a repost. This has been driving nuts for 2 days....


Brake lights dont work. Either pushing pedal or turning on lights.

Turn signals work just fine.

Cab/cargo/3rd brake light on back of cab doesn't work either.

I have checked/done the dollowing:

- Checked Brake pedal switch for continuity. Tested fine.
- put multi meter on wiring all the way back to brake lights. No drop in voltage.
- changed bulbs. #3157 dual filament.
- positioned steering wheel all the way up and all the way down as suggested on here. No change.
- checked multi function switch (turn signal switch) for wiring issues. None found.
- kicked rear quarter panel for caveman adjustment out of frustration. No change.

What am I missing?
Please help if you can. I'm a contractor and every day I can't drive is money lost and another day behind schedule I get.

Thanks in advance!

 

I don't see where you addressed the possibility of a lost ground.
Any circuit has to have a complete path from battery + back to battery -.
If you have full voltage at the lamp sockets the ground is missing for some reason.
Test supply a ground at the socket and see if the lamp lights.
A place to check is the harness plugup along the driver side frame that supplies the rear lighting and any frame or panel ground connections.
Good luck.

 

Thanks man. Didn't think of that. I will do so and post back.

forgot to add that I checked the fuse as well and it was good.

 

something does not add up... brake lights don't work but turn signals do ? But you have 12 volts on the brake wire at the socket at the rear of truck ? ......... I guess all that's left is the ground, but why do the turns work ?

 

I don't believe the brake lights should come on by turning on the lights.

But what are we working on?

 

Sorry, forgot to post that too.

it's a 1997 ford f150 4.6L ext cab off road


I have no idea how the turn signals work and the brakes dont. It's the same bulb, just a double filament.

checked grounds and they all seem okay.

I have 12 volts all the way to the brake lights on drivers side, so good there.


one thing...the brake pedal switch was showing 28-32 volts. Is this normal?

the top wire on brake pedal switch is always hot but the bottom one only kicks on when pedal is depressedoing. Don't know if this helps you all help me.

thanks again everyone. I'm so frustrated by this issue.

 

Culprit: #13 fuse was blown

Fix: install new 15 amp mini fuse (blue)

earlier I had checked #18 fuse to the brake lights (15 amp mini) and it was good. Did not know that Brake On/Off (BOO) [brake pedal switch] #13 (also 15 amp mini) had its own fuse that was used with the cargo high stop lamp on the back of the cab. Huge oversight that I didn't know of. Apparently the current runs through the cargo stop lamp first then to the BOO then to the multi switch on column then to the rear lights.

Still don't know how the turn signals were working if the multi switch gets power from the BOO and cargo stop lamp but I don't care, this suckered is FIXED!

 

It doesn't work that way. The BOO switch gets power from F13. The multi-function switch SWITCHES the power from the BOO switch or the flasher unit to the bulbs.

 

I would guess that the light you had was TAIL LIGHTS and the 12V power you measured was to the tail light... The SECOND filament is the BRAKE and the TURN and they get power down the SAME WIRE from the multi function switch. ------------- or maybe it is possible if there are TWO power sources to the multi switch, but you would not have 12 v at the bulb in the BRAKE application.

 

Bingo! Fuse #13 feeds the BOO switch and from the BOO switch power goes to the Brake side of the MFS.


Fuse #1 feeds the Turn/Hazard side of the MFS.


(Therefor, if you step on the brakes with the Hazards on, the brake lamps will not pulse until you let off the brakes. Meanwhile, the front Turn Lamps will continue to pulse while the brakes are applied.)

 

Turn signals, tail lights, cab lights all work including the 3rd break light but the tail break lights do not work. Checks the bulbs, replaced fuses 13, 15 and still nothing. Ideas?

 

check the Brake-light switch from the brake pedal

 

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