Getting brake lights to work

[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 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.

[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

[RustyPile]

Originally Posted by waters5

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

Something I've noticed about your links.. They all relate to 1973 and up models.. Do you realize you're posting in the '67 - '72 truck forum??? If you're working on a '67 - '72 and trying to install a '73 - up harness, this could be the root cause of your problems.

On the other hand, if you're working on a '73 - up, you might get more and better responses if you get an administrator to move your portion of this thread to a more appropriate forum...

[PanhandleShantyman]

OP, my curiosity is sparked by two interesting things you note:
1: turning on the headlights causes the problem
2: disconnecting the turn signal makes the problem go away

My '69 had an issue where:
1: when I turned my headlights on, the turn signal INDICATOR in the dash came on inappropriately.
2: If I disconnected the turn signal, this problem went away.

I regrounded the turn signal and this problem went away. It made me think that somehow, with power going through the headlight, that current was somehow finding ground through the switch or something, through a path that went through the indicator lamps and activated them... or maybe that explanation could be way off , but anyway I wonder if whatever the true explanation is, maybe something similar is happening for you, and the problem might go away if you improve the ground to your turn signals.

It'd be easy enough to test. Run a jump wire from your turn signal lamp assembly to ground, and see if the problem goes away!

[zicc1835]

subd ....good info here I too am having some rear signal and brake light issues