Taillight question

"Just Jeepin'" (macintux)
03/12/2019 at 21:33 • Filed to: None

I first posed this a few months ago but I’m still perplexed and keep seeing this so I’ll ask again. Does anyone know whether some cars will compensate for a failed running light by turning on the brake light instead?

I feel like I see mismatched running lights too often to be just random electrical problems, but I just dunno.

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DISCUSSION (20)

facw > Just Jeepin'
03/12/2019 at 21:40

I’ve never heard of this, and I can’t say I’ve seen it either. My car compensates for having a taillight out by having four taillights.

My X-type is too a real Jaguar > Just Jeepin'
03/12/2019 at 21:41

Depends in some cars both filaments light for the brakes so yes.

Just Jeepin' > facw
03/12/2019 at 21:42

Three red lights in back is about four too few, but that seems like what we’re mostly stuck with.

Just Jeepin' > My X-type is too a real Jaguar
03/12/2019 at 21:43

Can you clarify?

facw > Just Jeepin'
03/12/2019 at 21:46

Well that’s just the taillights. Obviously I’ve got brakes, turn signals, reverse lights, and one rear fog (I think there’s a bulb opposite the rear fog for symmetry, even though it doesn’t, and isn’t supposed to do anything). I think there also may be some side markers that are part of the rear light clusters.

My X-type is too a real Jaguar > Just Jeepin'
03/12/2019 at 21:49

Pre LED cars had combination brake tail lights, there were 2 filaments in each bulb, when you stepped on the brakes in most cars both filaments lit up. So if one was burned out the other would still light. If it was the brake filament that burned out the tail light filament would light when the tail lights were off.

Not all cars lit both filaments. So on some cars yes others no.

Boxer_4 > Just Jeepin'
03/12/2019 at 21:55

You’re not imagining things:

(Skip to 10:45 if it doesn’t start there)

The examples use cars with two sets of brake lights, but I can imagine that your described scenario happens, too.

RallyDarkstrike - Fan of 2-cyl FIATs, Eastern Bloc & Kei cars > facw
03/12/2019 at 22:03

Fun fact, on my 2009 Accent hatch there are 4 bulbs per side at the back: 2 running/brake, 1 reverse and 1 amber turn signal per side .

In North America, all four rear main lights function as both brake AND running lights, but in Europe, only the top two are brake/running lights and the bottom two are wired as rear fogs! :)

Kinja'd!!!

Svend > Just Jeepin'
03/12/2019 at 22:29

My first Skoda Superb got around a til light bulb out by having so many.

The car said we had a til light bulb out but on a dull morning, with the tail lights lit, I honestly couldn’t tell if one had blown.

Kinja'd!!!

Two of those bulbs double as brake lights.

Future Heap Owner > Just Jeepin'
03/12/2019 at 22:32

Unrelated, but yesterday I told the guy driving the Ram that pulled out of the grocery store lot in front of me that two of his tail lights were out, which he was unaware of. I never did this before you joined Oppo.

Just Jeepin' > Future Heap Owner
03/12/2019 at 22:52

Keep up the good fight. Sysiphus got nothin’ on us.

Just Jeepin' > My X-type is too a real Jaguar
03/12/2019 at 22:54

This is the opposite, however.

What I see while driving : one brake light, one running light.

What I see when stopping: two brake lights.

MiniGTI - now with XJ6 > Just Jeepin'
03/12/2019 at 23:58

Sure it’s not a rear fog (hate except when really needed)?

Just Jeepin' > MiniGTI - now with XJ6
03/13/2019 at 00:00

Yes, absolutely certain. First time I ran across it was an old American minivan, and I typically see it on simple 3-light setups (not counting reverse lights): brake, running, turn signals all combined.

MiniGTI - now with XJ6 > Just Jeepin'
03/13/2019 at 00:02

I saw a somewhat recent Honda van once where the brakes were wired into the yellow turn signal bulbs so anything’s possible.

gogmorgo - rowing gears in a Grand Cherokee > Just Jeepin'
03/13/2019 at 00:16

I’m not sure this is what’s going on in your scenario, but it’s a thing that can happen with dual-filament bulbs.

In case you were unaware , most dual-filament bulbs will only have a single ground point, whether only one ground path leaving the bulb, or multiple paths from the bulb converging in the bulb’s socket. In the event you have only one filament illuminated but there’s higher resistance in the ground path between the bulb and chassis than there is in the bulb’s other filament (generally a broken or corroded wire) , the current will find its way to ground via the other filament, and possibly other lights in the same curcuit, sometimes with some pretty interesting results.

Just over a month ago, we had an International in the shop where there was a problem with a common ground for the all the lighting on the front of the truck, so the headlights, clearance lights, and work lights were all grounding through the turn signal bulbs. This meant that when you hit the turn signals, when they blinked on it interrupted the ground path, so when the signals were receiving power, every single light on the front of the truck blinked out, and back on again when the signals weren’t illuminated.

Svart Smart, traded in his Smart > Just Jeepin'
03/13/2019 at 00:42

I have seen a first-gen Audi Q7 use, on one side only, the auxiliary light down in the rear bumper in lieu of the tailgate-mounted LED brake light, which had failed — but this was in daytime conditions.

I think I’ve seen a recent GLE/M-Class use a running light as a brake light, but not a brake light as a running light, as you asked about.

pip bip - choose Corrour > Just Jeepin'
03/13/2019 at 05:16

some high end Euros do (iirc)

LimitedTimeOnly @ opposite-lock.com > pip bip - choose Corrour
03/13/2019 at 08:28

Yes, I have seen (older) Volvos and Mercedes-Benz sedans with a different bulb turned on in a different part of the taillight enclosure when the standard running light bulb appears to be out.

pip bip - choose Corrour > LimitedTimeOnly @ opposite-lock.com
03/13/2019 at 08:37

bmw too