No brake lights

[Crewcaber]

So my 70’ crew cab has power brakes.
I have no power to the wire under the frame. I have a test light to the wire.
I’ve checked/Hooked up
I’ve put a test light on the power on the proportional valve and no power there.
I’ve grounded the master to the body as well. (Read somewhere it needs that)
I’ve got power to running lights and turn signals.
All I see is one wire going to the proportional valve.
Any help????

[712edf]

I believe the wire from the proportioning valve is for the brake warning light IN THE DASH. When the valve is off center (from fluid loss) it grounds the wire out & illuminates the brake warning light in the instrument cluster. Has nothing to do with the brake lights at the rear of the truck.

Do the hazard lights work?

First place to check for power is the switch which I think is on or near the brake pedal arm. At least it is on later trucks. One wire should be hot at all times. When the pedal is pressed the switch makes contact inside & the other wire gets power.

If no power at switch then start checking around fuse box & wiring.

Bucky

[Crewcaber]

Good to know!!!!
I’ll check that.
Turn signals work can’t say about the hazards.

[Crewcaber]

So. Dug under the dash and found that switch cleaned everything. Verified the hot and boom. Brake lights to the wires going out the back of the truck.
Buuuuut……
Someone before me cut the wires at the half way point.
It has 4 wires
Yellow
Green
Black
Brown

Green was right turn
Brown is running lights
Black is reverse lights I believe.
This is where it’s tricky. Yellow had power at both brake lights AND LEFT TURN.
How can I splice the brake lights to the right side of the truck without them also coming on with the left turn signal???

[712edf]

Green is one side. Yellow is the other.

Brown is tail lamps, park lights on front.

You could have a messed up hazard switch. I believe brakes lights go through this.

Your turn signals were working when you began, correct?

Bucky

[712edf]

Also you want the hazard switch OFF when testing the other areas for power.

Bucky

[PwrWgnDrvr]

Brake and turn signals are the same filament in the bulb at the rear. Yellow left, green right. They go thru the sig switch on the column.

[Crewcaber]

I’ve got power through yellow and green with turn signals.
How do I wire the bulbs so the filament works with brakes lights to both but one side with turn signals??

[Crewcaber]

I’ve got constant hot on a blue wire to the brake proportional valve

[Crewcaber]

Got it.
Re tested right blinker with brakes. BOTH get hot with brakes through blinker wires.
Makes sense now.

[BigBlockTrucks]

Got it.
Re tested right blinker with brakes. BOTH get hot with brakes through blinker wires.
Makes sense now.

Double check to make sure they have a good ground also.
But, sounds like you have it figured out.
Happy motoring!

[PwrWgnDrvr]

I’ve got power through yellow and green with turn signals.
How do I wire the bulbs so the filament works with brakes lights to both but one side with turn signals??

You don't wire anything. The turn signal switch on the column does that.