Brake Light/Rear Turn Signal Issue

[dz1087]

Just found out I have an issue with my rear brake lights/turn signals. The problem is when the right turn signal is on, and the brakes are applied, the left brake light turns off. Otherwise, everything works as it should. Both brake lights come on fully when the brake is applied. When the lights are on, the rear lights come on fine. Also, when the lights are on, and the right turn signal is activated, and the brakes are applied, the left parking light coil (the dimmer of the two in the rear bulb) will stay on, but the brighter brake light coil will not illuminate.

No issues when the left turn signal is activated - everything works.


Specs:
AAW wiring harness, installed last spring.
Bed center crossmember is grounded to frame.
Frame is grounded to engine.
Engine is connected to battery negative terminal.

Thoughts? Is there an easy way to determine I need a new turn signal switch vs a ground issue?

[67C10Step]

Sounds like a ground issue to me. I'd probably start by running a dedicated ground wire from each tail light to a known good ground area and see if the issue remains or clears up.

[pjmoreland]

It could also be that your turn signal switch contacts are gummed up.

[dz1087]

Just got done testing the tail light assemblies. Both have good ground, verified with multimeter with positive probe in the sockets and negative probe touching the housing.

Leaves me thinking is the switch, unless you fellers can think of anything else.

[Andy4639]

Have you checked the bulb? Have you checked the socket? I have seen the sockets get wear and the bulb want stay in place. I've seen the bulb tabs fall off and not work. Check all the easy stuff first. Have you done any work on any of the electrical system latey?
Your brake lights and turn signals all go through the wiring harness in the steering column. Could be a wire issue outer sleeve worn through touching metal are a turn signal cam problem. Could be the bulb itself even. I'd start at the column harness connector and probe the wires that go to the rear of the truck with it in the position that gives you the problem and probe the wires and see if it does the same there if not keep moving towards the back of the truck and see where it starts being a problem.

[dz1087]

The sockets are new and work fine, bulbs are fine.

[RustyPile]

Originally Posted by dz1087

Just got done testing the tail light assemblies. Both have good ground, verified with multimeter with positive probe in the sockets and negative probe touching the housing.

Leaves me thinking is the switch, unless you fellers can think of anything else.

That test only verifies good contact between the socket and housing.. You also need good grounding contact between the housing and bed, between the bed and frame, and lastly, between frame and negative battery post.. A quick method to test for loss of ground is to run a long jumper directly from the negative battery post and the bulb socket.. Don't depend on twisting the wires to make contact.. Use those larger alligator clips found on small battery charger/tenders.. Hook up the jumper and try those lights again.. If they work as they should, you definitely have a grounding issue..

[REDROCKER652002]

My son's truck had a somewhat similar issue. It turned out the connection wire at the bulb housing had come loose. In other words, the three wires that go into the plastic plug that plugs into the back of the taillight, one of those wires had come loose and was not making a connection. Not sure if that is even close to what you are experiencing, but what the heck. I figure I would throw it out there.

[dz1087]

Originally Posted by RustyPile

That test only verifies good contact between the socket and housing.. You also need good grounding contact between the housing and bed, between the bed and frame, and lastly, between frame and negative battery post.. A quick method to test for loss of ground is to run a long jumper directly from the negative battery post and the bulb socket.. Don't depend on twisting the wires to make contact.. Use those larger alligator clips found on small battery charger/tenders.. Hook up the jumper and try those lights again.. If they work as they should, you definitely have a grounding issue..

I disagree. The circuit would have to be complete in order for the multimeter to sense a difference in the potential energy between the socket and the housing. If the housing were not grounded, the multimeter would have read zero.

Regardless, with the two-wire setup on the tail lights (one pos wire for the parking lamps and one for the brake lights), a ground failure would prevent the bulbs from turning on at all. I've got good brake lights and good parking lights on both sides. The left brake light fails to come on only if the right turn signal circuit is activated.

[Andy4639]

Originally Posted by dz1087

I disagree. The circuit would have to be complete in order for the multimeter to sense a difference in the potential energy between the socket and the housing. If the housing were not grounded, the multimeter would have read zero.

Regardless, with the two-wire setup on the tail lights (one pos wire for the parking lamps and one for the brake lights), a ground failure would prevent the bulbs from turning on at all. I've got good brake lights and good parking lights on both sides. The left brake light fails to come on only if the right turn signal circuit is activated.

There again the turn signal connector looking like the problem. Check it out.

[dz1087]

Originally Posted by Andy4639

There again the turn signal connector looking like the problem. Check it out.

I'll dig in to it today. If the problem manifests at the connector, is it safe to assume switch, or are there other grounds up in there that may be buggered up? The steering column is about the only thing I haven't torn apart on this truck yet.

[Andy4639]

Originally Posted by dz1087

I'll dig in to it today. If the problem manifests at the connector, is it safe to assume switch, or are there other grounds up in there that may be buggered up? The steering column is about the only thing I haven't torn apart on this truck yet.

The only ground inside the steering column is for the horn button.

[dz1087]

Wanted to close out this thread. Got back from deployment and ordered a new switch to put in. Switch fixed it right up. No more issues.

The old one could have possibly been cleaned, however the plastic was cracking around the stalk pivot anyway. Biggest gripe was I had to ditch the AAW pigtails that were supplied with my new harness and wire the new switch in directly. In the future I may put them back in, but for now, it’ll do.