View Full Version : brake light wiring info needed
02-18-2006, 09:35:45 AM
I am doing some wiring on my car and looking at the diagrams from this site. I dont see how the brake switch on the peddle ties in. The diagram for the trunk shows ground, brown, yellow, only three wires doing four functions.
So I am trying to determine how this works under the dash to control the turn signals and brake lights.
Car is a 1970 RS.
What am I missing? :confused:
Any help is appreciated.
02-18-2006, 10:19:40 AM
The GM wiring diagrams are very poorly drawn. Apparently GM didn't have anybody working for them who understands electricity.
The brown wire is for tail lamps only and will be powered anytime the headlights or parklights are on.
The yellow (left side) and the dark green (right side) wires are for signal lights and brake lights. They did both functions by running power through the brake pedal switch, and from there to the signal switch in the steering column to power both left and right side signals when the brake pedal is depressed. The yellow and dark green wires can be powered individually by the signal switch for left and right signalling.
Your brake switch should have only two wires. One will have +12 on it all the time from the fuse panel. The second wire will get +12 when the brake pedal is depressed, and that wire feeds into the steering column to supply the turn signal switch the voltage to apply both signals for braking.
The black wire is the ground for all functions.
02-18-2006, 02:12:28 PM
Good information. One more question. How can I test the functions of the turn signal switch?
ETA. Just checked things out and when I push the brake pedal it blows the fuse.
Any suggestions where to look?
the wiring from the dash to the trunk is new. rest is old under the dash.
02-18-2006, 10:42:45 PM
unplug the new wires going to the trunk and see if it still blows the fuse. that way you have a starting place.
02-19-2006, 02:44:30 PM
Disconnected the harness to the rear and it still blows fuse if I push brake pedal or turn on hazards.
Could it be in the directional switch?
Cant really see where the wires run. Don't know If I should pull the steering wheel and check that out.
02-19-2006, 02:53:38 PM
disconnect the wiring harness under the steering column that connects the turn signal switch and see if it still blows the fuse.
02-21-2006, 02:18:08 PM
Will try that as soon as I get back out there.
02-23-2006, 01:00:50 PM
Unplugged the harness at the steering column. Does not blow fuses now.
Where is the next logical spot to check out?
Thanks everyone. :bowtie:
02-23-2006, 01:23:58 PM
could be in the column...what fun!
do you have the factory shop manual? is it tilt wheel?
do you have an ohm meter (digital volt meters usually have this)? and do you know how to use it? if so, with the turn signal switch harness unplugged, measure the resistance from each wire in the TS swtich to ground, if any are low resistance then that wire is shorted out somewhere.
02-23-2006, 04:40:01 PM
Don't have a manual, guess I should get one.
It is not a tilt wheel.
So pull the steering wheel and check wires with a meter? I have a multimeter and know how to use it.
02-23-2006, 04:43:47 PM
No, don't pull the wheel yet! first use the meter to check each turn signal switch wire (at the plug in connector) to see if it's shorted to ground. If one is, then you need to pull the wheel and the switch, which is a bit tricky if you've never done it. If you don't find any shorts there, then disconnect the battery, and check the wires that go to the front turn signals (light blue, dark blue) to see if they're shorted (might pull the bulbs first?). Also give a good visual inspection of all the wiring you can see, look for pinched wires, or pulled out ends or whatever you can find.
02-23-2006, 07:13:38 PM
Will try to get time to check this weekend.
02-23-2006, 08:17:25 PM
Just something else to think about, when I was putting mine together I decided to put in a tilt wheel, the only problem was that the donor car had cruise (and mine doesn't) so the brake hot wire was directed through the cruise control circut and the brakes wouldn't come on, it was an easy fix cause I just bypassed that part of the circut. I would check to be sure the column switch is the right one also. Just a suggestion, be gentle guy's this is my first post
02-23-2006, 09:11:40 PM
Just remember, just because you pulled the wires for the turn signal switch, doesn't mean that the problem is in the switch.
Those wires also feed into the dash and on to the lights, the problem could also be there.
Kinda unlikely though.
I will try to post my wiring diagrams for the 70.