I broke my new truck

[Bextreme04]

This is not correct. The turn lights and brake lights are the same single bulb on each side. Two wires (yellow and green) to make both brake lights light up. If you turn on the the turn signals, then power is interrupted to that side when the brakes are applied.

Brown wire feeds all the tail lights and license light. Light green wire feeds both reverse lights.

Crap, you're right... although it is still probably a single wire issue since neither brake nor turn works on just the left side. That points to a problem with the yellow wire. The connector will be a round plug behind the bumper near the drivers side frame rail. That bundle runs all the way up the drivers frame rail, under the brake booster, and into the firewall connector.

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[Juan Cano]

I found the wire harness right next to the bumper. It has a square connector to connect to the wires coming from the cab. My 86 has a bulb for brake/light, a bulb for blinker/hazard, and a bulb for reverse.

Either way I tested continuity from the socket connector to the light sockets in the housing. I got continuity for the rear light and the reverse bulb (which matches because those two work). I didn't get continuity for the wire that feed the brake light bump (the bulb has 2 metal bumps at the bottom, seems one for light and one for brake) and no continuity for the blinker light socket. So perhaps the sockets are bad which is easy enough to fix. Or maybe there's a break on the wire of course.

 

[Juan Cano]

@Bextreme04 Thank you for that amazing diagram! And @Turbo4whl for clarifying.

Probably will start with replacing the bulb sockets and the shady enclosure. You can see in this hack job of a tailight that they felt duct tape was a key ingredient and it also looks like the enclosure had a date with a hacksaw????? I should open the other one too I guess.

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[Bextreme04]

@Bextreme04 Thank you for that amazing diagram! And @Turbo4whl for clarifying.

Probably will start with replacing the bulb sockets and the shady enclosure. You can see in this hack job of a tailight that they felt duct tape was a key ingredient and it also looks like the enclosure had a date with a hacksaw????? I should open the other one too I guess.

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Wow, that's rough! They make some pretty nice actual LED taillight assemblies if someone wanted to go LED... that is definitely not the best way to do it. You can get new ones from a bunch of places...

 

[Juan Cano]

Here is where I am with this today. I realize like someone mentioned that the brake wire is also the wire that controls the blinker. On the driver side rear is the yellow wire. Per the awesome diagram. I cut the light socket out and tested for power coming into the yellow wire when the brake is depressed and nothing. I also went under the truck and unplugged the connector that connects the rear harness to the front of the truck. I tested the front connector on the yellow wire and I get nothing. I do get 12V if I touch the green brake wire for the passenger rear.

So this has go me thinking that maybe it's not an issue at the end but at the start of this circuit. The rear brake harness, where does it connect to the front? Is it in the engine compartment?

 

[Turbo4whl]

The turn signal switch is where the brake light feed is switched to both rear lights or interrupted when the turn lever is moved. Back probe the turn switch at the connector plug at the bottom of the steering column.

Yes, some trucks have a seperate connector for the rear lights at the firewall.

 

[Juan Cano]

oK; so I changed the light socket but that didn't do anything. I went under the steering wheel and used a test light to see if the blinker was working from over there. This is the connector that connects to the wires that come out of the horn assembly. The yellow connector made the test light blink so the signal is being sent right?

It shouldn't be this hard....

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[Juan Cano]

OK; so a victory and a step backwards. I went down the rabbit hole and checked wire continuity from the firewall to the rear harness connector, and it's fine. I then decided since the rear wire harness had a bunch of splices and also a tow hitch wire kit that is not used, to just cut it all out. So I got rid of the connectors and the tow hitch harness, and was essentially left with the four wires coming from the front and the 4 wires going to the lights (well they still go up to a T and then split off). I twisted the matching color wires together, and the blinkers work!

But, the brake lights for BOTH sides stopped working. If I turn the lights ON the bulbs work, and the Reverse works.

When I removed the tow hitch harness, there was a ground attached to them and I cut that off. But looking at the diagram, the tail light housings are grounded to the body. And if they weren't grounded, it doesn't seem the blinkers or running lights would work right?

The Hazard lights work; the Brake fuse is fine; I checked the brake pedal switch and it's getting 12V when I depress it.

Why did the brake lights stop working? Gotta do some googling.

 

[SrMousse]

I can't help but read this and laugh... only because I've been there. My primary culprit wasn't a hack of a back yard "mechanic" but rather mice... and it felt like every time something shorted and I fixed it, the next things shorted too... it was a nightmare... but hey, I did get good at wire troubleshooting as well as splicing... What doesn't kill you... am I right?

 

[Juan Cano]

@SrMousse Totally. I have learned so much! But I just want this truck running so I can drive it!!!!!

 

[Snoots]

Tail light housings do NOT give you a ground. Go back and check for ground at the bulb socket.

 

[Juan Cano]

I fixed it!!!! So it seems the reason that the brake lights were not working is that the connection at the end of the horn switch (which is brand new), the white wire was not getting a good connection. The white wire controls the brake light. On the female end of this connector, I had replaced the white wire pin myself and it's like these 2 little jaws and apparently they were spread out too much so not making contact on the other end.

So silly.

I figured it out by testing if there was power to the white wire on the brake switch, and there was, then on the horn switch connector on the white wire I didn't get any power. I un-coupled it and immediately I could see those tiny jaws laughing at me, HA HA HA HHA HA

I tightened them with a knife, put the connectors back together and that was it. Hoping to hit Brimfield this weekend on the truck!!

 

[Juan Cano]

I jinxed it. All effed up again. On the dashboard the right hand blinker is on all the time, the left blinks. But on the actual tailights, nothing blinks.

Super happy for 1.5 hrs.

 

[80BrownK10]

I jinxed it. All effed up again. On the dashboard the right hand blinker is on all the time, the left blinks. But on the actual tailights, nothing blinks.

Super happy for 1.5 hrs.

Light not burned out? That normally in a functioning truck means a bulb is burnt.

 

[Juan Cano]

@80BrownK10 I don't think so. The light bulb works, just doesn't blink. I

t was working 100% minutes early. The two things that changed were: I joined the rear harness wires to the rest of the harness by using splices, but that's like 4 wires into matching colors. And second one is that I drove it and moved the steering wheel around. Maybe something got moved when turning the steering wheel since that's the turn signal switch I just replaced.

I know, makes no sense.