Getting brake lights to work

[kcstreetracer]

I'm trying to get my brake lights working. It has all new harnesses but brake lights wont work. What circuits have to be complete for them to work? Like on headlights they won't work without the dimmer. Is there anything like that on the brakes? Sorry for the newbie question I'm new at this lol

[Ol Blue K20]

Is the turn signal switch plugged in?

[BigBird05]

Power for the brake lights come from the brake light switch. Power into thw switch is orange.Power out of the switch is white. Goes into the steering column up to the turn signal switch. If the turn signal switch is not turned to either the left or right then the power goes out the left wire ( yellow )and right wire (dark green )thru the firewall connector back to the frame connector then out to the left and right sides. No lights is usually caused because of a bad ground. Start by checking for a bad ground. If the ground is good (do you have running lights ), then go to the brake light switch and start checking for power. Then work your way thru the system till you find the bad connection.

[Minkota]

also, confirm you have a good grounds at the tail/brake lights. I just went thru this myself.

[kcstreetracer]

Turn signal harness plugged in, and I have running lights. Ill check Grounds

[kcstreetracer]

Could a bad flasher cause no brake lights?

[PanhandleShantyman]

Originally Posted by kcstreetracer

Could a bad flasher cause no brake lights?

I just replaced a bad flasher. It hadn't affected the brake light function on my truck.

[Caddylackn]

I second the search for good grounds.

A DC circuit is a loop and the 12 volts and current has to be able to get all the way back to the battery through the negative terminal for it to work. So battery must be properly grounded to the frame, then all accessories grounded to the frame. The cab must be grounded to the frame as well, as many accessories are grounded behind the dash to the sheet metal.

[kwmech]

make sure the 4 wire connector is pushed in TIGHT at the firewall and at the back of the frame

[kcstreetracer]

It has all new grounds. Battery to frame and engine. Cab to frame
Bed to frame. Ran grounds for the light buckets to frame. New oe style wire harness front to back. Checked connections they are tight. New brake light switch even tried 2 of them. Still can't get brake lights or turn signals. I have running lights. Its a new column as well so turn signal switch is new. Its a el cheapo column I wonder if the turn signal switch is bad by chance. All I need is brake lights so I can take it for a drive lol! Whole truck is new ground up I'm ready to drive this thing!

[pjmoreland]

Make sure the battery has a path to the chassis as well. This is usually through the negative battery cable to the engine, then from the back of the engine to the firewall, and then from the cab floor to the front right cab support on the chassis.

Also, did you check voltage along the circuit that BigBird05 described? These checks will need to be done with the brake pedal pressed down. Check for voltage at every connector in the brake light circuit.

[Rich72C10]

My vote is your turn signal switch. I have had a bear of a time with mine, though it wasn't ever my brake lights or at least not the problems like you are having.

I got a shorten tilt (I had a non-tilt column) last year from a now banned forum user. Straight off the bat the turn single wouldn't cancel... 20 minutes of tweaking I got that to work. Then after a few months I started to blow fuses, which did take out the brake lights and inside cab light. I think I might have been driving around for weeks before I noticed I didn't have brake lights. I still randomly turn on my cab light to see if the fuse has blown again!

I got a replacement from GMCsPaul that has the red hazard pull. Seems a bit of debate if the tilt had the red pull switch or black one (but GMCsPauls says it is correct for our trucks). Though it did have the half-moon original type connector, so no adapter was needed (I hate adapters). But this one wouldn't flash the brake lights, unless I was pushing in hard on the hazard switch. I was a little put off that GMCPauls wouldn't stand behind what they sold me, so that was $50 bucks down the drain.

So I got my 3rd one (again from GMCPauls), at least this time I was a pro getting it installed. Now everything to do with the signal switch is perfect! It even has a better feel when I engage the turn signals. I guess 3rd time's the charm!

[gmc684x4]

Have you checked the switch on the brake pedal to insure it operates correctly?
I know its been mentioned #1 through 3 electrical issues on a vehicle are grounds

Did you also switch to led bulbs ?

[rockyrivermark]

Don’t chase your tail and just throw parts at it.
A simple $15 light tester will tell you a lot.
Make sure test light is connected good ground and verify
Then Test for power at brake bulb socket. If power there then fix ground. Remember you need a ground jumping cab to bed.
If no power at socket work backwards testing for power on circuit along the way.
test power in and out of the brake switch.
Test power on both sides of the fuse. Good fuse on a rusted socket is not unusual.
The cheap tester is the best 12v diagnostic tool you can own.

https://www.amazon.com/dp/B07Q3622FT...ZZ5K0Z54VR8JZY

Mark

[BigBird05]

with the column harness connected check to see if you have power on the white wire With brake pedal depressed . Check on the column side of the connector. If you do check to see if you have power on the dk green and yellow wires. Check on the column and the dash wiring side of the connector. If you have power there then move to the fire wall connector. Check on the under hood side of the connector. Then move to the rear harness connector located on the rear frame crossmember. If you have power there then remove the light bulbs and check the pig tail inside the tail light housing. If you have power there then it has to be a ground issue.

[lil hoodlum]

I had recently bought another project, a 1968 C20 and it was having tail light/ brake/ signal issues. I made sure the brake light buckets were making proper electrical connectivity, i.e., metal to metal contact. Next, I replaced the rear light harness as mine was so old and hacked into. I tried to work with what I had but not until I replaced it with a reproduction harness did it work properly.

[waters5]

Im kinda stumped and was wondering if anyone had this problem. In day time my LED brake lights work just fine no issues. When I have the ignition off and lights on the tail light are one and get super bright when brakes applied. Everything working normal, soon as I turn the ignition on with the headlights the taillights get very bright when I apply the brakes the taillights don’t change since the lights are already at their brightness setting.
I have a new wire harness from front to back with Dakota digital setup is there a setting or something i am missing that can be causing this?

[RustyPile]

Originally Posted by waters5

Im kinda stumped and was wondering if anyone had this problem. In day time my LED brake lights work just fine no issues. When I have the ignition off and lights on the tail light are one and get super bright when brakes applied. Everything working normal, soon as I turn the ignition on with the headlights the taillights get very bright when I apply the brakes the taillights don’t change since the lights are already at their brightness setting.
I have a new wire harness from front to back with Dakota digital setup is there a setting or something i am missing that can be causing this?

Have you tried removing the LEDs and putting the incandescent bulbs back in?? If the problem persists, read post #14 and follow those test procedures..

[dmb]

Originally Posted by rockyrivermark

don’t chase your tail and just throw parts at it.
A simple $15 light tester will tell you a lot.
Make sure test light is connected good ground and verify
then test for power at brake bulb socket. If power there then fix ground. Remember you need a ground jumping cab to bed.
If no power at socket work backwards testing for power on circuit along the way.
Test power in and out of the brake switch.
Test power on both sides of the fuse. Good fuse on a rusted socket is not unusual.
The cheap tester is the best 12v diagnostic tool you can own.

https://www.amazon.com/dp/b07q3622ft...zz5k0z54vr8jzy

mark

x2

[Palf70Step]

you didn't mention, but do the turn signals work. If they do and brakes don't then I'd say the issue is in the brake switch. If they don't then wiring, grounds and turn signal switch is the areas needed traced through.

[waters5]

Originally Posted by Palf70Step

you didn't mention, but do the turn signals work. If they do and brakes don't then I'd say the issue is in the brake switch. If they don't then wiring, grounds and turn signal switch is the areas needed traced through.

With headlights off brake lights and turn signals work like normal, when im driving and turn the headlights on turn signals still work but the rear lights go on like the brakes are fully engaged.

[RustyPile]

To solve this problem, you'll definitely need a wiring diagram, and the knowledge to read it. If this is beyond your skill level, find someone locally to help you.

There are 2 power sources for the rear turn signals and brake lights and both of them enter the turn signal switch at 2 different points.. Starting at the brake light switch, the orange wire (hot all the time) brings power to the switch. When the pedal is depressed, that power is applied to the white wire where it is carried to the turn signal switch. When the T/S switch is OFF, this power passes through the switch and back to the brake lights through the dark green wire (right side) and yellow wire (left side) brake lights..

The 2nd power source is the purple wire (hot only when ignition switch is ON) coming from the flasher unit on the fuse box. It goes to the turn signal switch and is picked up as a power source only when the turn signal switch is activated for either side.. From there power is passed along the dark green wire or yellow wire, depending on whether RIGHT TURN or LEFT TURN is selected...

None of the circuits are connected to any other lighting system.. If the wiring harness has errors in its construction or there are errors in its installation, there is NOT a set of instructions for locating these errors. Only diligent troubleshooting while referring to the wiring diagram will find the problem.. The problem can be exasperated by a change in the color coding of the wires... I have the tools, skill, and knowledge to construct wiring harnesses using proper gauge and color coding.. Therefore I have zero experience with any of the aftermarket harnesses.

[waters5]

The truck has a new American autowire harness installed with LS3 motor and all new LED lights. I have tested the brake switch with continuity to verify it’s functioning. When I unplug the column turn signal wiring lights go to normal. When I swapped to a new turn signal switch the lights behave the same.

When I unplug the brake switch verified I have hot power on orange wire and no power on white. With ignition on the white wire on the brake switch connector shows a dim light on tester.

When I test the rear body harness wiring mentioned in the thread previous tips everything tested fine.

Headlight switch off with ignition on: brake lights and blinkers work normal
Headlights switch on: brake lights work normal
Headlights and ignition on: only blinkers work and lights are on as if brakes are engaged.

http://http://https//api.americanautowire.com/shopify/instructions/92970223%20510347%20IN%202.0.pdf

[RustyPile]

Originally Posted by waters5

The truck has a new American autowire harness installed with LS3 motor and all new LED lights. I have tested the brake switch with continuity to verify it’s functioning. When I unplug the column turn signal wiring lights go to normal. When I swapped to a new turn signal switch the lights behave the same.

When I unplug the brake switch verified I have hot power on orange wire and no power on white. With ignition on the white wire on the brake switch connector shows a dim light on tester.

When I test the rear body harness wiring mentioned in the thread previous tips everything tested fine.

Headlight switch off with ignition on: brake lights and blinkers work normal
Headlights switch on: brake lights work normal
Headlights and ignition on: only blinkers work and lights are on as if brakes are engaged.

http://http://https//api.americanautowire.com/shopify/instructions/92970223%20510347%20IN%202.0.pdf

That is the messiest wiring diagram I've ever seen..

Have you checked both sides of the T/S plug for correct wire position?? What were the results when you removed all those LEDs and put the incandescent bulbs back in???

Have you checked to see if some random wire is erroneously connected to something else, or not connected at all?? The clue to this is the brake lights being on with the ignition switch and headlight switch being ON... These 2 circuits are 2 entirely separate and different circuits, NOTHING is shared... NOTHING connected to the headlight switch is also connected to the brake lights nor turn signal lights.

[waters5]

Originally Posted by RustyPile

That is the messiest wiring diagram I've ever seen..

Have you checked both sides of the T/S plug for correct wire position?? What were the results when you removed all those LEDs and put the incandescent bulbs back in???
http://https://api.americanautowire.com/shopify/instructions/92970194%20510350%20IN%201.0.pdf
Have you checked to see if some random wire is erroneously connected to something else, or not connected at all?? The clue to this is the brake lights being on with the ignition switch and headlight switch being ON... These 2 circuits are 2 entirely separate and different circuits, NOTHING is shared... NOTHING connected to the headlight switch is also connected to the brake lights nor turn signal lights.

Im working to trace out the wiring currently for the dash wires to see if there is a wire landed in the wrong place on the digital Dakota box or harness.
Americanautowire has their wiring diagram broken down or in a full harness view

https://americanautowire.com/collect...y-truck-510347

https://api.americanautowire.com/sho...20IN%201.0.pdf