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:metal:

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.

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. :metal:

Re: No brake lights but switch is getting power
 

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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

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.

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

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

Re: No brake lights but switch is getting power
 

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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

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.

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.

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.

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.

Re: No brake lights but switch is getting power
 

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

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.