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

Peanut74 · 12-17-2021, 12:18 AM

Ok, I got the diagram downloaded. So at least I can now trace wires and know where they go. Tomorrow I plan on plugging the steering column temporary to see if the brake lights work or not.

Does anyone know where I can get a matrix showing the switch positions during the various operations?
EX: brake lights: white power: to green and yellow

**LockDoc** · 12-17-2021, 01:26 AM

-
Here is one for the headlight switch. I don't know of one for the turn signal switch but there may well be one.

LockDoc

Peanut74 · 12-17-2021, 11:08 AM

Well pugging in the steering column solved my power issue so thanks everyone on that point. However, my LED bake lights did not come on. I have read in some cases that you need to add a resister to get them to work right. So do I need to add a resister or is that to make the flasher work for the turn signals?

By the way this is what I have so far on my switch matrix's. If I screwed it up please let me know.

toolboxchev · 12-17-2021, 01:27 PM

Short answer is most of the time the turn signal switch goes bad. Yet you do have to do all your wire tracing and circuit testing.

Peanut74 · 12-18-2021, 11:39 AM

Well I got the brake lights working. The drivers side factory socket had a broken wire at the connection point. So I wired in a new 3 prong connector and everything is working fine.

Now on to the backup lights. The PO wired in a switch rather than having it wired like normal. So I will be tracing that one down now. Right now I can say I don't have power to his switch with the key turned to run or pulled out.

Peanut74 · 12-19-2021, 10:03 PM

Turned out the fuze was blown. After some wire tracing and about 7 blown fuzes I narrowed it down to the rear tail light harness. Haven't had time to finish figuring it out. But I am pretty sure the short is in one of the factory bulb sockets.

RustyPile · 12-20-2021, 01:09 AM

Quote:

Originally Posted by Peanut74

Turned out the fuze was blown. After some wire tracing and about 7 blown fuzes I narrowed it down to the rear tail light harness. Haven't had time to finish figuring it out. But I am pretty sure the short is in one of the factory bulb sockets.

I use this tool to help me locate electrical shorts. https://toolaid.com/product/25100

Peanut74 · 12-21-2021, 07:54 PM

Thanks Rusty I will need to check it out. Would make finding the shorts a lot easier.

12-16-2021, 09:11 PM	#1
Peanut74 Registered User Join Date: May 2018 Location: Prattville, AL Posts: 590	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 million pieces down from a bazillion) 1989 Toyota DLX pickup "The Hulk" 2012 Jeep JKU "Crush" 1976 Chevy short bed with a 327 and 3 on the tree (Sold it to buy the Blazer) 1971 Chevy Blazer (Sold it)

12-16-2021, 09:18 PM	#2
RustyPile Registered User Join Date: Dec 2017 Location: Elkhart, Texas Posts: 1,647	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: 590	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 million pieces down from a bazillion) 1989 Toyota DLX pickup "The Hulk" 2012 Jeep JKU "Crush" 1976 Chevy short bed with a 327 and 3 on the tree (Sold it to buy the Blazer) 1971 Chevy Blazer (Sold it)

12-16-2021, 09:50 PM	#4
LockDoc The Older Generation Join Date: Aug 2006 Location: Montezuma, Iowa Posts: 25,400	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: 2,211	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: 8,487	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

12-17-2021, 12:18 AM	#7
Peanut74 Registered User Join Date: May 2018 Location: Prattville, AL Posts: 590	Re: No brake lights but switch is getting power Ok, I got the diagram downloaded. So at least I can now trace wires and know where they go. Tomorrow I plan on plugging the steering column temporary to see if the brake lights work or not. Does anyone know where I can get a matrix showing the switch positions during the various operations? EX: brake lights: white power: to green and yellow __________________ -------------------------------------------------------- 1967 C10 "Snowball" (Currently in a million pieces down from a bazillion) 1989 Toyota DLX pickup "The Hulk" 2012 Jeep JKU "Crush" 1976 Chevy short bed with a 327 and 3 on the tree (Sold it to buy the Blazer) 1971 Chevy Blazer (Sold it)

12-17-2021, 01:26 AM	#8
LockDoc The Older Generation Join Date: Aug 2006 Location: Montezuma, Iowa Posts: 25,400	Re: No brake lights but switch is getting power - Here is one for the headlight switch. I don't know of one for the turn signal switch but there may well be one. LockDoc Attached Images __________________ Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 -

12-17-2021, 11:08 AM	#9
Peanut74 Registered User Join Date: May 2018 Location: Prattville, AL Posts: 590	Re: No brake lights but switch is getting power Well pugging in the steering column solved my power issue so thanks everyone on that point. However, my LED bake lights did not come on. I have read in some cases that you need to add a resister to get them to work right. So do I need to add a resister or is that to make the flasher work for the turn signals? By the way this is what I have so far on my switch matrix's. If I screwed it up please let me know. Attached Images __________________ -------------------------------------------------------- 1967 C10 "Snowball" (Currently in a million pieces down from a bazillion) 1989 Toyota DLX pickup "The Hulk" 2012 Jeep JKU "Crush" 1976 Chevy short bed with a 327 and 3 on the tree (Sold it to buy the Blazer) 1971 Chevy Blazer (Sold it)

12-17-2021, 01:27 PM	#10
toolboxchev Registered User Join Date: Jul 2015 Location: 2nd left past the stump on a dirt road. Posts: 2,629	Re: No brake lights but switch is getting power Short answer is most of the time the turn signal switch goes bad. Yet you do have to do all your wire tracing and circuit testing.

12-18-2021, 11:39 AM	#11
Peanut74 Registered User Join Date: May 2018 Location: Prattville, AL Posts: 590	Re: No brake lights but switch is getting power Well I got the brake lights working. The drivers side factory socket had a broken wire at the connection point. So I wired in a new 3 prong connector and everything is working fine. Now on to the backup lights. The PO wired in a switch rather than having it wired like normal. So I will be tracing that one down now. Right now I can say I don't have power to his switch with the key turned to run or pulled out. __________________ -------------------------------------------------------- 1967 C10 "Snowball" (Currently in a million pieces down from a bazillion) 1989 Toyota DLX pickup "The Hulk" 2012 Jeep JKU "Crush" 1976 Chevy short bed with a 327 and 3 on the tree (Sold it to buy the Blazer) 1971 Chevy Blazer (Sold it)

12-19-2021, 10:03 PM	#12
Peanut74 Registered User Join Date: May 2018 Location: Prattville, AL Posts: 590	Re: No brake lights but switch is getting power Turned out the fuze was blown. After some wire tracing and about 7 blown fuzes I narrowed it down to the rear tail light harness. Haven't had time to finish figuring it out. But I am pretty sure the short is in one of the factory bulb sockets. __________________ -------------------------------------------------------- 1967 C10 "Snowball" (Currently in a million pieces down from a bazillion) 1989 Toyota DLX pickup "The Hulk" 2012 Jeep JKU "Crush" 1976 Chevy short bed with a 327 and 3 on the tree (Sold it to buy the Blazer) 1971 Chevy Blazer (Sold it)

12-21-2021, 07:54 PM	#14
Peanut74 Registered User Join Date: May 2018 Location: Prattville, AL Posts: 590	Re: No brake lights but switch is getting power Thanks Rusty I will need to check it out. Would make finding the shorts a lot easier. __________________ -------------------------------------------------------- 1967 C10 "Snowball" (Currently in a million pieces down from a bazillion) 1989 Toyota DLX pickup "The Hulk" 2012 Jeep JKU "Crush" 1976 Chevy short bed with a 327 and 3 on the tree (Sold it to buy the Blazer) 1971 Chevy Blazer (Sold it)



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