Park light issue (LED bulb)

kardain

Original poster
Member
Dec 16, 2011
557
Ok, so I've been trying to fix this minor cosmetic annoyance for a little while and all I've managed to do is chase gremlins.

When the park lights are off and the brake pedal depressed, between 4-5 volts backfeeds to the park light circuit. This backfeed causes the last two rows of LEDs to illuminate on the front bulbs. They then turn off when the brake pedal is released.

I've ruled out the following changes (tested one at a time and tested once with all changes except the front LED bulbs):

*Modified tail light boards as being the source as this continues when I swap back in the OEM boards.
*Rear LED bulbs have been ruled out. It continues when the incandescent bulbs are swapped in (both in the OEM and modified boards).
*Flasher. It persists with the OEM and LM487 flasher
*Front LED bulbs. Here is where it gets interesting.... I tested several sets of LED bulbs, including transferring the middle pair from the rear to the front. Depending on how the bulbs were manufactured, either all diodes light up dimly or just a row or three.
*Rear load resistors, removed them, no change to issue.
*Jettt DRL killer. Temporarily set back to stock, no change.
*Unplugging the rear circuit boards altogether didn't change anything. Issue persists.
*Added 6ohm-50w load resistors to the brake light circuit in the rear (at recommendation of v-leds), no change. I pulled the resistors off my cavalier for this test rather than purchase new.

The bulbs that I am running currently are all from V-LEDs (some test sets up front were purchased from superbright)

The front bulbs are 3157 5k white/amber type two switchbacks
Rear brake/turn when rear OEM board is used is 3157 7w red.

So now I'm a bit lost. I'm not opposed to swapping back to incandescent in the front, but only as a last resort.

anyone have a nudge in the fix direction they want to share?
 

Sparky

Member
Dec 4, 2011
12,927
I'll bet yours is wired weird like mine is. GM crossed some wires in places and made things work a little funny at times.

I noticed on my stock tails before I put in LED tails that when the hazards were on the running lights would very dimly flash too from a backfeed.

Everyone talks about VW's poor electrical engineering, but GM did some pretty stupid things themselves at times as well :crazy:
 

kardain

Original poster
Member
Dec 16, 2011
557
Up up and away!

The park light bleed also goes through the trailer harness.... Bad brake switch perhaps?
 

Blckshdw

Moderator
Nov 20, 2011
10,682
Tampa Bay Area, FL
You've ruled out most of the things I thought of, but I had a similar experience. When I put the 194 switchbacks in, a diode was missing from my polarity switcher. So when I activated the turn signal on either side, it would backfeed through the parking circuit and make all of them flash, including my mirror LED strips and liftgate light bar (both on the trailer parking light circuit) :duh:

If the problem still persists with the tail lights unplugged, I'm not sure where else the parking signal and brake signal could cross paths. Guess the next step is to throw some stock bulbs up front and see what happens with those.
 

kardain

Original poster
Member
Dec 16, 2011
557
I can't find any common area either...

Looked through the schematic to see... The parks are commanded on by the BCM... It activates a relay in the rear fuse block when the headlight switch is either manually turned on or the auto on feature engages. Pin 30 is tied to the front, rear and trailer park fuses. The park lights don't even go through the flasher, whereas the brake does (pin b)

Aside from the ground wire in the rear boards, there is no common path for power.

I'll check the rear boards again in a few, unplug them and check for backfeed with the park relay and fuses removed.

If that's the case, the only path to the parks should just be the ground wires, meaning the bulbs should not illuminate due to polarity.
 

kardain

Original poster
Member
Dec 16, 2011
557
So I pulled the park light relay, no change. With the relay out, pulled the trailer park fuse, no change. With those two out pulled the front park fuse, they stopped lighting up with the brake depressed.

This was with the rear boards unplugged....

I'm wondering if 1) there might be a cross in the trailer circuitry or 2) there is a way to run the front park lights as drls using the JS drl killer relay thingy, or 3) there is a problem with the rear bulbs themselves.... I'm researching option 2... Rain stopped me from testing 3.
 

Blckshdw

Moderator
Nov 20, 2011
10,682
Tampa Bay Area, FL
kardain said:
So I pulled the park light relay, no change. With the relay out, pulled the trailer park fuse, no change. With those two out pulled the front park fuse, they stopped lighting up with the brake depressed.

This was with the rear boards unplugged....

I'm wondering if 1) there might be a cross in the trailer circuitry or 2) there is a way to run the front park lights as drls using the JS drl killer relay thingy, or 3) there is a problem with the rear bulbs themselves.... I'm researching option 2... Rain stopped me from testing 3.

You said you put stock bulbs back in and the problem persisted with the (un)modified boards right? Do the front lights light up when the park and trailer park fuses are in, but the front park fuse is out? :undecided:

As for #2... :popcorn: :biggrin:
 

kardain

Original poster
Member
Dec 16, 2011
557
Sometimes I don't explain things too well.... Especially later in the evening.

I put stock 3x57 bulbs back up front thinking it may be enough resistance to bleed the extra voltage... Also unplugged the rear boards in case there was a possibility of number 3 being true. There was not enough voltage to turn on the incandescent 3x57, but enough for the led 194 side markers in the headlight. Nothing was plugged in the trailer plug.

My trailer has led lights in sealed housings (meaning I can't change those), to test the trailer circuit I unplugged the front park fuse, and with the trailer fuse in and the rear boards unplugged, got bleeding through the trailer markers. Unplugged the trailer marker fuse and nothing lit on the trailer.

With the front park fuse unplugged as well as the rear boards unplugged, nothing lit up front.... So the problem is pre-marker fuse... "where" is the problem? The only common point I can find for brake and park is the ground. For the #3 test, I was going to swap in incandescent 3x57 in the rear, but while tracking some down it started raining buckets so decided to hold off on that one. Also in case there was a issue with the rear bulbs, unplugging the boards takes that out of the loop.
 
May 22, 2012
117
I was reading this post with great interest. I had a similar issue with my 1991 s10 blazer. I would hit the brakes and the parking lights would come on. Turn out it was a bad hazard warning switch. replaced it and the problem went away.
 

kardain

Original poster
Member
Dec 16, 2011
557
Somehow the problem fixed itself, with a side effect.

The right rear reverse/turn completely failed due to a poor solder joint within the bulb. I swapped out the modded boards for the OEM ones until I can get another set of switchbacks to replace. Somehow, I lost reverse lights altogether (no blown fuses for reverse) regardless of LED bulb orientation, the indicator lights on the 4x4 selector switch and the little green light on the headlight switch indicating auto-on. All were functioning properly prior to switching the boards over.

Whatever caused all those to go out at once fixed the "park on when brake depressed" issue... just need to trace back and find what killed the reverse lights. I'm in no hurry though, reverse lights are overrated

Such is the life of a modder :smile:
 

Blckshdw

Moderator
Nov 20, 2011
10,682
Tampa Bay Area, FL
The 2nd best problems, are the ones that fix themselves (the 1st best, are the ones that never happen in the first place) Maybe in another week, those other issues will fix themselves too? :undecided:
wish.gif
 

kardain

Original poster
Member
Dec 16, 2011
557
I know, right? Now if the blown intake gasket on my Sunfire can just fix itself, that will save a 10 hour repair. LOL
 

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