Author Topic: LED issues  (Read 3419 times)

Offline rrigg

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LED issues
« on: October 29, 2017, 11:58:51 AM »
Hi All,
So happy to find a forum dedicated to my favorite era of trucks!
Say, I am having a couple of lighting issues related to a LED changeover that I need some advise on.

My Truck:
1984 GMC Sierra Classic heavy half with towing package - 6.2 diesel - 2 wd - longbed

I am bringing this truck back to life after 15 years of sitting in a machine shed - have owed it since 1984 and it is in excellent mechanical shape. Just gave it a fresh paint job and reworking the interior a bit.

My two issues:
I have replaced every bulb on the truck with an LED equivalent except the headlights (yes even the instrument cluster bulbs), and have nice LED compatible flasher units for turn and hazard..... but two issues have come up - note, I am almost certain the lighting was working correctly prior to the switch-over

1 - front side marker lights..... worked fine with small led's until I put the led's up front in the park/turn light. Now they are not working (or are so dim as to be almost not visible). Something to do with needing resistors to ground I think.... but not sure exactly what to do.

2 - Rear issues with blinkers.... both sides flash regardless of which direction you choose. The front flashes correctly, the rear has both sides flashing all the time.

I have good electrical skills and a good voltmeter.... I am just at a loss as to what to test and do LOL

Thanks!!

Online bd

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Re: LED issues
« Reply #1 on: October 29, 2017, 12:21:16 PM »
Welcome to the Forum from Central California!

Read through, side lights flash with indicators ( LED).  Check all of the vehicle grounds, especially between the rear lamps to the bed, frame and battery.  See Ground for additional details.  Remove the hazard flasher to see if the symptom of all rear lamps flashing disappears.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Captain Swampy

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Re: LED issues
« Reply #2 on: October 29, 2017, 05:06:17 PM »
I agree, sounds like a ground issue.
1987  350TBI 700R4  4X4  4.56 gears  33" BFG All Terrain


http://forum.73-87chevytrucks.com/smforum/index.php?topic=32209.0

Offline VileZambonie

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Re: LED issues
« Reply #3 on: October 29, 2017, 06:54:01 PM »
Try flipping the bulbs 180° for the ones that do not work.
,                           ___ 
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              ⌠ŻŻŻŻŻ'   [☼===☼]
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74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline rrigg

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Re: LED issues
« Reply #4 on: June 02, 2018, 09:18:13 PM »
UPDATE:
Fixed the front side marker issue with the resistor method - works perfectly now up front....

But I am pulling my hair out trying to solve the rear blinker issue up top in the original post.
Additional info:
"ghost in the machine" issue that I am thinking is related: With truck off and keys removed, if I turn the blinker on left or right, and then step on the brake pedal, the low coolant, fasten seat belt, and glow plug light all "blink" at about the rate of the flasher.... but the turn signal indicator on the dash stays solid  the whole time.

With a trailer attached the blinker does the same of the trailer - both sides flash with blinker on in either direction.
Same behavior occurs with the rear wiring harness completely unplugged - and checking with a voltmeter in the socket at the rear - both sides flash voltage


Tried removing the hazard flasher - no change (both sides flash with turn signal going... but front blinkers and dashboard indicators behave as expected)
Replaced Brake light switch - no change
Checked voltage at the bulb sockets - no big drops (not sure what is considered a big drop, but they were within a few tenths of a volt)
Checked grounds - not sure I am doing it correctly... but I checked resistance between the various body parts, the ground at each rear tail-light, battery to frame, etc.

Any ideas - I have no path forward at this point.
Any help would be greatly appreciated.
Cheers






« Last Edit: June 02, 2018, 09:21:20 PM by rrigg »

Offline Rapid Roy

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Re: LED issues
« Reply #5 on: June 02, 2018, 09:54:42 PM »
Welcome
1974 Cheyenne 10 LWB STOCK 350 W HEI /TH350/AC/4 BBL Quadrajet
Mopar by Birth
Chevy by Choice

Offline Chuck Step-a-side

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Re: LED issues
« Reply #6 on: June 03, 2018, 09:51:49 AM »
After you get all the LED lamps working, You'll need to purchase a LED flasher relay because the LED lamps draws low voltage and cause hyperflashing. You might have to reverse the LED flasher blade connection to get the flashers to operate properly (make a wire jumper to reverse). I have done this to my truck and it works.

Offline rrigg

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Re: LED issues
« Reply #7 on: June 03, 2018, 11:00:09 AM »
Thanks Chuck!
I actually did replace both turn signal and hazard flasher relays with LED polarity independent relays - still have the issue (and I had the issue with stock flasher too as well as blinking fast)
This is what I used:
https://www.amazon.com/gp/product/B01GIU9M0Y/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1

Cheers

Online bd

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Re: LED issues
« Reply #8 on: June 03, 2018, 01:36:32 PM »
Begin by making absolutely sure that the turn signal switch is not internally shorted and the dark green and yellow rear turn signal wires are not shorted together.

Otherwise, all of the symptoms you described point to less than perfect ground connections between the rear lamps and battery negative.  LEDs don't require much voltage to illuminate.  They are current dependent requiring ~0.03 ampere to illuminate fully, rather than voltage dependent devices.  Slight resistance in the ground path that won't appreciably interfere with incandescent lamp function can cause LEDs to illuminate.  Since the dash lamps are also LEDs, minuscule current feedback to the front of the vehicle will illuminate the dash lamps, as well.  In other words, a nearly unmeasurably poor ground at the back of the vehicle can cause a low current loop from B+ through the wiring to the rear lamps then, since the rear lamps are grounded but not perfectly grounded, a current divider is created at the ground connection and some of the current flows back up the "unpowered" wiring to the dash, backfeeding the dash harness and connected LEDs through the closed turn signal switch.

Under the circumstances, I don't believe that installing resistors is a viable solution.  Because of the length of the wire run between B- and the rear lamps, trying to establish a "perfect ground" may prove frustrating, although that would be optimum.  Your best bet may be to install 1N4003 - 1N4006 series diodes in each of the light green, dark green, yellow and brown power wires feeding the rear lamps, cathode band to the rear lamps.

Incidentally, when troubleshooting routine electrical issues, use a good DVM to measure voltage drops rather than an ohmmeter to measure resistance.  Unless you have a lab grade meter and the acquired skill to use it, a typical ohmmeter does not provide sufficient sensitivity to accurately measure the low resistance values that can severely impact continuity.
« Last Edit: June 03, 2018, 01:58:17 PM by bd »
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline rrigg

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Re: LED issues
« Reply #9 on: June 13, 2018, 06:08:59 PM »
Thanks BD
Following your advise I have solved the issue - it was indeed the turn signal switch in the column that was the issue. strange that the front blinkers worked correctly.
After replacing this switch in the column my issue is no more :)
Cheers

Online bd

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Re: LED issues
« Reply #10 on: June 13, 2018, 07:46:56 PM »
Happy to assist!
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)