Brake switch swap only fixed one side

[EricCruzzin]

Hey everyone, I’m havin issues with my driver side brake/turn signal. Originally I had no brake lights at all so I swapped the brake switch and the passenger side brake and signal started working, but the damn driver side still doesn’t work, I get lights when I turn my lights on, but no hazards, brake, or turn signal on driver side rear at all. I tried swapping bulbs with passenger side and even swapping the entire assembly over and it worked fine on passenger side but driver side still had nothing. Any ideas?

 

[1998_K1500_Sub]

Hey everyone, I’m havin issues with my driver side brake/turn signal. Originally I had no brake lights at all so I swapped the brake switch and the passenger side brake and signal started working, but the damn driver side still doesn’t work, I get lights when I turn my lights on, but no hazards, brake, or turn signal on driver side rear at all. I tried swapping bulbs with passenger side and even swapping the entire assembly over and it worked fine on passenger side but driver side still had nothing. Any ideas?

What year and model vehicle? It appears from past posts, you've got a 1997 K1500.

The rear left and right taillights share a common ground (at least in 1998 and I assume other years), so if the right side is working then the ground is evidently suitable, and thus is suitable for the left side as well. Too, you said the left side taillight does work and the turn signal / brake / hazard (the "bright light") does not work. So let's consider the ground as "OK" for the moment.

You mentioned "driver rear". Do hazard and turn signals "not work" on front, on back, and on the indicator in the gauge cluster for the left (driver's) side? Asking it differently, do any of these three work for the left side, while others do not work for the left side?

Is the CHMSL ("third eye" stoplight) illuminating?

If none of the left side "bright lights" are illuminating, it may be the turn signal/hazard switch (see wiring diagram for 1998, attached). That switch is in common with the right and left side, so if the right's working and the left isn't, that switch may ("may") be the culprit, i.e., the contacts within that pass power to the "bright" bulbs are open-circuit.

If some of the left bulbs are working but others on the left are not, then there's likely some sort of wiring issue / ground issue downstream from the turn/hazard switch. We'll entertain that thought when the time comes.

Since you swapped rear taillights left / right (so you said), and the left still didn't work, that's reason for us to believe the problem lies further upstream, towards the turn/hazard switch, and not with the connector / circuit board / bulbs.

Later, we'll consider next steps, focusing on the turn/hazard switch.

 

[EricCruzzin]

What year and model vehicle? It appears from past posts, you've got a 1997 K1500.

Sorry didn’t realize I forgot to put make and model, I’m in a 95 k1500 now things didn’t work out with the 97 unfortunately.

The rear left and right taillights share a common ground (at least in 1998 and I assume other years), so if the right side is working then the ground is evidently suitable, and thus is suitable for the left side as well. Too, you said the left side taillight does work and the turn signal / brake / hazard (the "bright light") does not work. So let's consider the ground as "OK" for the moment.

You mentioned "driver rear". Do hazard and turn signals "not work" on front, on back, and on the indicator in the gauge cluster for the left (driver's) side? Asking it differently, do any of these three work for the left side, while others do not work for the left side?

Ok so when I turn the hazards on illuminate on both sides in the front and only on the passenger side on the rear but everywhere on the instrument cluster. For the turn signals, I have turn signals illuminating on both sides in front, but only on passenger side in rear.

Is the CHMSL ("third eye" stoplight) illuminating?

Yes when brake is depressed third light is illuminated

If none of the left side "bright lights" are illuminating, it may be the turn signal/hazard switch (see wiring diagram for 1998, attached). That switch is in common with the right and left side, so if the right's working and the left isn't, that switch may ("may") be the culprit, i.e., the contacts within that pass power to the "bright" bulbs are open-circuit.

I will check this next, the wiring diagram is new to me so I’ll need to do some research so I can read it properly and apply it

If some of the left bulbs are working but others on the left are not, then there's likely some sort of wiring issue / ground issue downstream from the turn/hazard switch. We'll entertain that thought when the time comes.

When I turn the light switch on (as if I was driving at night) the middle bulb (which is the bulb that acts as signal/brake) lights up so the bulb works but not in all the ways it’s intended to (ie brake/signal)

Since you swapped rear taillights left / right (so you said), and the left still didn't work, that's reason for us to believe the problem lies further upstream, towards the turn/hazard switch, and not with the connector / circuit board / bulbs.

Later, we'll consider next steps, focusing on the turn/hazard switch.

I appreciate the super thorough response. Im going to look up where the “plunger” the wiring diagram is talking about is located and make sure everything matches up.

 

[EricCruzzin]

It got late on me but I found something concerning that could be causing the issue. There’s a connector near the rear diff that’s melted pretty bad, I’m trying to find a replacement online but may end up going to the junkyard for the sake of time

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[1998_K1500_Sub]

That ground connection in the background of your picture doesn't look the best.

What happened to cause that connector's plastic body to deform?

I have to look-up that connector, I don't recognize it offhand. Just guessing, it's either for the rear taillights / trailer wiring, or a fuel pump / gas gauge.

Based on your recent observations above (post #3), the problem lies in the wiring downstream from the turn/hazard switch, i.e., that going to the left rear "bright" filament.

 

[GoToGuy]

You mentioned earlier about about replacing the bulbs in tail lights, but no mention of checking if there was power to bulb sockets. Easy check with test light.
The tail/ brake light lights are not hard to figure out. If you do the most basic troubleshooting.
You can get a new shell for the connector at a auto parts store. If the pins are good just depin and pin into new shell. Then no splicing or shrink tube or other weak spot.
Green Yellow Brown ? Same colors they been using long time for tail lights wiring. Turn/brake, running.
Third brake gets signal power before brake/ turn signal power.
You have turn signal and brake on one side, that should told you the problem is most likely down stream of cab. Then use your test light.
If you don't check the basics first, you run the chance of following an endless troubleshooting/ diagnostic trail with no end in sight.

 

[1998_K1500_Sub]

There’s a connector near the rear diff that’s melted pretty bad, I’m trying to find a replacement online but may end up going to the junkyard for the sake of time

Consider removing the connector completely and soldering the wires together.

The wires may be in poor condition, they’ll often oxidize within the insulation (visible as greenish specs among the strands in the wire). You may choose to replace some of the wire as well on account of it.

 

[89RCLB]

If it were me I would source a replacement connector from the bone yard and solder it in. That connector is there for a reason.

 

[1998_K1500_Sub]

If it were me I would source a replacement connector from the bone yard and solder it in. That connector is there for a reason.

Valid point.

I was thinking that connector’s sole purpose was to facilitate manufacturing / assembly, and for that reason likely best eliminated at this point. That’s why I told him to “consider” removing it.

OP, act as you see fit. KEEP IN MIND that you may need to remove the bed someday (e.g., to replace the fuel pump), so if this connector makes that easier you may wish to replace it / not eliminate it.