No brake lights but switch is getting power - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Peanut74 · 12-16-2021, 09:11 PM

I am now in the wiring stage of my trucks rebuild. As a beginning I decided to check the brake lights first. They did not go on when brake pedal was pushed. I did check the switch out and it is working fine. I then checked the taillights for good grounds and power. They do have good grounds but no power. I next checked the harness plug under the bed. No power on any of the terminals. I did some searching here and found this "The brake lights and all other lights for the rear of truck and front run through the turn signal switch". Which might explain my issue since I don't have the steering column installed yet. Sorry for being long winded but what to make sure everyone all the information.

So my questions are:
1 = Does the steering column indeed need to be wired up before I can check the brake lights?
2 = Does anyone have a good wiring diagram that I can download?
(I have found a couple but when I zoom in I can't make anything out.)

Thanks in advance for the help

RustyPile · 12-16-2021, 09:18 PM

Yes, the steering column harness has to be plugged into the main harness. Go to the ELECTRICAL forum on this site. you'll find wiring diagrams for all our trucks.

Peanut74 · 12-16-2021, 09:43 PM

Thanks for the info Rusty. That would explain why nothing seemed to be working past the cab. I hate not having a wiring diagram as I am old school and like to trace the wires to find the issue.

**LockDoc** · 12-16-2021, 09:50 PM

-
Here are the diagrams.

http://67-72chevytrucks.com/vboard/s...d.php?t=185856

If you will notice in the first two posts, under the wiring image it says "Here is the link for the largest version". Click on the "4200x2550" in each post for the larger versions of the diagrams.....

LockDoc

**Accelo** · 12-16-2021, 10:02 PM

The tail light should work, if the light switch is installed. Same with the side markers. Front parking lights & side markers will not work unless they are grounded through the bumper or an aux ground. The brake lights are also the turn signals and require the column to be plugged in. Or you can test it with just the switch connected.

**kwmech** · 12-16-2021, 10:06 PM

When you step on the brake the white wire gets power and goes into the turn signal switch, from there the power goes through the turn signal wires---green (rt) and yellow (lt) back down the column and to the rear

12-16-2021, 09:11 PM	#1
Peanut74 Registered User Join Date: May 2018 Location: Prattville, AL Posts: 611	No brake lights but switch is getting power I am now in the wiring stage of my trucks rebuild. As a beginning I decided to check the brake lights first. They did not go on when brake pedal was pushed. I did check the switch out and it is working fine. I then checked the taillights for good grounds and power. They do have good grounds but no power. I next checked the harness plug under the bed. No power on any of the terminals. I did some searching here and found this "The brake lights and all other lights for the rear of truck and front run through the turn signal switch". Which might explain my issue since I don't have the steering column installed yet. Sorry for being long winded but what to make sure everyone all the information. So my questions are: 1 = Does the steering column indeed need to be wired up before I can check the brake lights? 2 = Does anyone have a good wiring diagram that I can download? (I have found a couple but when I zoom in I can't make anything out.) Thanks in advance for the help __________________ -------------------------------------------------------- 1967 C10 "Snowball" (Currently in a thousand pieces down from a bazillion) 1989 Toyota DLX pickup "The Hulk"

12-16-2021, 09:18 PM	#2
RustyPile Registered User Join Date: Dec 2017 Location: Elkhart, Texas Posts: 1,854	Re: No brake lights but switch is getting power Yes, the steering column harness has to be plugged into the main harness. Go to the ELECTRICAL forum on this site. you'll find wiring diagrams for all our trucks.

12-16-2021, 09:43 PM	#3
Peanut74 Registered User Join Date: May 2018 Location: Prattville, AL Posts: 611	Re: No brake lights but switch is getting power Thanks for the info Rusty. That would explain why nothing seemed to be working past the cab. I hate not having a wiring diagram as I am old school and like to trace the wires to find the issue. __________________ -------------------------------------------------------- 1967 C10 "Snowball" (Currently in a thousand pieces down from a bazillion) 1989 Toyota DLX pickup "The Hulk"

12-16-2021, 09:50 PM	#4
LockDoc The Older Generation Join Date: Aug 2006 Location: Montezuma, Iowa Posts: 25,825	Re: No brake lights but switch is getting power - Here are the diagrams. http://67-72chevytrucks.com/vboard/s...d.php?t=185856 If you will notice in the first two posts, under the wiring image it says "Here is the link for the largest version". Click on the "4200x2550" in each post for the larger versions of the diagrams..... LockDoc __________________ Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 -

12-16-2021, 10:02 PM	#5
Accelo Senior Member Join Date: Mar 2015 Location: washington Posts: 2,302	Re: No brake lights but switch is getting power The tail light should work, if the light switch is installed. Same with the side markers. Front parking lights & side markers will not work unless they are grounded through the bumper or an aux ground. The brake lights are also the turn signals and require the column to be plugged in. Or you can test it with just the switch connected.

12-16-2021, 10:06 PM	#6
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,656	Re: No brake lights but switch is getting power When you step on the brake the white wire gets power and goes into the turn signal switch, from there the power goes through the turn signal wires---green (rt) and yellow (lt) back down the column and to the rear



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