rear brake bulb keeps blowing (2 Viewers)

[Shipwreck]

This is driving me nuts.
My passenger (R) brake light keeps burning out. But just the brake filament. The running light filament in the bulb is fine. I've tested voltage at both circuits coming in to the bulb and measure 11.4 - 11.6 V with ignition off and 11.6 - 11.7 V with the engine running. Both the brake circuit and running light circuit read about the same. The drivers side (L) taillight works normally reads about the same voltage. The turn signal and reverse bulbs are OK and work normally. The third brake light on the hatch works.

Here is what I've done aside from measuing voltage
I can replace the bulb and press on the brake pedal and it works normally.
I can start the engine, press on the brake pedal and it works normal.
I can turn on the headlights and it works normal.
Once I start driving around, the bulb blows. It blows whether the headlights are on or not.

I completely disconnected my aftermarket trailer harness. No change.

I've traced wiring and continuity back to the BQ1 connector and cleaned the trailer socket.

I assume that I'm getting a voltage spike while driving, but I don't know how to diagnose that or measure it.
Any Ideas as to where I should look next?

 

[baldilocks]

Road vibration may be causing a short to ground on an exposed conductor. This could be time consuming to locate by visual inspection.

Does the bulb blow literally every time you drive the vehicle?

 

[Road Apple]

Have you installed LED’s recently? I’ve seen a couple post that they can cause issues with regular bulbs.

 

[Shipwreck]

Road vibration may be causing a short to ground on an exposed conductor. This could be time consuming to locate by visual inspection.

Does the bulb blow literally every time you drive the vehicle?

That's what I was thinking originally and why I inspected wiring back to the connector with the drivers side harness. It's a pain in the ass to pull OEM wrap and tape to look for breaks, so I haven't gone beyond that.
Yes, the bulb blows every time.
I've bought all the 1157 bulbs from the three auto parts stores near my house.

Have you installed LED’s recently? I’ve seen a couple post that they can cause issues with regular bulbs.

Nope. These are all regular incandescent.
I've had LEDs in my dash for 6-7 years without issue, and they are on a separate circuit.

 

[LandLocked93]

Just replace the harness that connects from inside the rear cargo area to the light housing.

 

[robnicko]

I had a similar issue on my runaround car with rear bulbs blowing frequently and my Dad said to wipe some grease on the globe contacts and around the base of the globe.
Those globes have been fine for a couple of years now.
I used wheel bearing grease FWIW

 

[Malleus]

That's what I was thinking originally and why I inspected wiring back to the connector with the drivers side harness. It's a pain in the ass to pull OEM wrap and tape to look for breaks, so I haven't gone beyond that.
Yes, the bulb blows every time.
I've bought all the 1154 bulbs from the three auto parts stores near my house.

Nope. These are all regular incandescent.
I've had LEDs in my dash for 6-7 years without issue, and they are on a separate circuit.

Based on what I've seen from unwrapping harnesses, I doubt it's a break in the insulation under the wrap. I'd bet it's the pigtail.

 

[80t0ylc]

I, also would bet it's a short in that bulbs circuit. It's current (amps) that's blowing that filament, same as a fuse. I've seen "twilight zone" type problems in light circuits before, several that replacing other bulbs in the same circuit fixed the problem. It's the multi-filament bulbs that can somehow get a short in them and cause havoc in trouble shooting. Short of a damaged harness or socket, that's about the only point where a short could happen. Cheap bulbs can be more trouble than they're worth. Looking briefly at the above schematic, I'd try replacing both bulbs (PS & DS) first. If that doesn't fix it, it might even be the stop light switch.

 

[MrMacdugal]

This may sound rudimentary, but you can simulate driving conditions by truning on the vehicle and operating the blinker. If it always works while you are not in motion, simulation motion by rocking the vehicle and/or jostling the wiring harness a bit. If you pop the fuse at that point, start looking at short to ground points.

In my 60, which i understand is much more basic that an 80 series, I had a front bulb socket shorting to ground on a piece of my light bezel that caused my rear lamp not to work properly.
It's not a big effort to replace all your lamp bulbs. Pull out all your lamps and dangle them from the vehicle, replace the bulbs and see if they all work properly while they are all NOT installed in your vehicle. Then you can also inspect all your plugs and connections as well.
It would probably take you 15 minutes to get all the lights removed, but still plugged in. Good Luck, hope you get it solved.

 

[Shipwreck]

I think I have this solved.
I cleaned up the ground for the brake lights that is located under the tailgate. Instead of just wire brushing the terminals like I did the first round, I cleaned, tapped the threads and put in a fresh, clean, shiny, zinc plated bolt.

Then the drivers side brake light blew. Arggh

This made me check voltage of the other things that were tied to that ground point. Turns out I had a short to ground from my cheapo Amazon backup camera that I installed a few years ago. That camera was acting wonky lately, especially after my 4 days on the Rubicon last month.
I think what was happening was that the camera was sending voltage to the ground point, but instead of ending there, due to a poor connection,the 12v went to the brake circuit. Once I reversed the truck, activating the backup camera, and then tapped the brake, the filament would blow. That is why everything tested ok in the driveway. It overloaded the filament only when I was reversing and hit the brakes.

Thanks for all the suggestions!

 

[80t0ylc]

Thanks for the followup! You showed persistence to solve this and that's what it takes, sometimes. Congrats