LED taillight problem - Hello, electrical experts!!!

M

Marshall V. Daut

Well-known member
"Amber" alert!!!
Well, I thought I had solved the constantly-on brake and taillight situation in a 1930 Roadster I am trying to straighten out. I replaced the incorrect brake pedal rod with one that has the flat stopper to push on the brake switch's plunger. After adjusting its throw to turn the brake light juice on and off, I find that the brake lights won't come on. The taillights are the LED conversion. The upper amber portion is supposed to have two brightnesses: one for operating at the same time with the red taillight (as the lights come from the manufacturer) and a brighter amber light for the brake lights. I have tried three brake light switches (all used) and found the switch is not the problem. If I swap wires from the new main wiring harness in back so that when the green wiring harness wire (the brake light) is temporarily connected to the black wire of the taillight portion (red lower lens), the lights come on (dual taillights) as brake lights. I have clipped the green wires inside the lights so that they operate as original, meaning red for taillight and amber for brake lights. Snyder's instructions tell how and why to so this.
So, power is getting to the taillights via the green brake light wire. But nothing happens when I connect green-to-green and black-to-black wires other than the red taillights turning on. In other words, the brake lights do not come on in the upper amber portion.
Because this car came to my friend with the taillights and even brighter brake lights constantly on due to the incorrect brake pedal rod, I am guessing the brighter amber electronics eventually burned out, or whatever kills diodes. I am also guessing the brake light function in these taillights is D.O.A. from constant use. Is there some way I can check the functionality of those little diodes in the upper portion of the taillights' motherboards with a voltmeter? If so, how would I do that, meaning dial settings and what kind of readings should I expect from a functioning motherboard? What would indicate dead diodes, etc.? Obviously, electrical issues are not my cup of tea.
Thanks in advance to you computer-minded readers!
Marshall
 
Marshall - I had what I think was this same problem with a new set of LED inserts from Snyders a couple of years ago. Only mine manifested itself on only one side, and it was within about 5 minutes of installation.

What I can suggest is that you take a known voltage source, establish a ground independant of the taillight on the car, and go directly from your source to the input wire on the LED insert. That should tell you whether the problem is within the assembly, or within the wiring (which includes the socket). You might also check the wire and socket at the taillight end with a VOM to be sure you're getting voltage and ground where you want it to be. If the issue is with the assembly, and the assemblies are within warranty, call Snyders and report the issue. That's what I did, and they shipped me a replacment on warranty immediately. As I noted above, this issue should not be an unknown.

However, the fact that you apparently have this issue in both assemblies (I assume duals, you do use the plural in your post) suggests to me that your issue may be in the wiring. Maybe a loose or corroded connection? Bad ground (I also found that the plugs within the LED inserts didn't fit tightly within the taillight socket, making a poor ground)?

FWIW, my original second LED insert, and the one I got as replacement, are still working fine two years in.
 
Our rear LEDs are not separated top and bottom, brake light on is the whole assembly. We did need ballast resistors for each side (6v) for turn signals but not with a 12 volt car. As stated, check the ground at the fenders, or if your set has a separate black ground wire which ours did.
 

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i assume that the car has signal lights through the taillights? if I remember correctly that's why you cut the wire in the taillight. if it does have signals could it be bad signal switch? if it doesn't, try reconnecting the wire in the light and see what happens. the upper half should be brake lights and lower half taillights.
 
Thanks for your suggestions so far. To fill in some more information, I had already done everything recommended before posting. Reconnecting the green wires only turned the upper amber portions (plural!) back on, as the lights came configured from the manufacturer. (See Snyder's attached instructions) No brake lights. Separating the taillight bodies from their brackets, of course, killed the ground. The lights went out, as they are supposed to do. Touching the taillight bodies again to their metal brackets turned on the red taillight portions ONLY. So, the grounding must be good.
I could understand if one upper light bulb socket did not fit well, but that shouldn't affect the second taillight. What are the odds that both sockets are bad or not grounding? Given the switching around and testing I did today, I still believe the brake light functions are dead in these lights. What else would explain the symptoms I have described? The problem must lie in the upper portions of the circuit boards. That's why I ask if there is a way to test each exposed diode on the circuit boards to see if they are dead? I do have a cheapie voltmeter that came with a soldering iron kit, but it might as well be a piece of NASA space shuttle equipment as far as my electronic competency goes. :) I need a SIMPLE step-by-step explanation of how to check the circuit board diodes, not the oddly-phrased foreign language instruction sheet that came with the voltmeter. "Ground to earth"????
M.
By the way, I deep-sixed the unbelievably poorly-wired turn signal mess that was confusing everything electronic. Who in the world would have thought the turn signals could have ever functioned the way things were wired and without the required ballasts for each LED taillight?
 

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Just a thought here, have you tried switching the leads on the taillight with the ones on the wiring harness? if you switch them and hit the brake, the taillights should come on and you know the brake switch circuit is ok. it should also prove your theory that the brake light circuit in the lights are dead without using the meter.
 
Yes, that was one of the first things I did after adjusting the new pedal brake rod. That's how I determined that the brake light switch was good. The red taillight portions lit up with that temporary wire hook-up. I just can't get the amber portions to light up. :(
M.
 
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it sounds like you're on the right track. I think you're going to wind up replacing those units and all should work fine. JMO of course.
 
"I think you're going to wind up replacing those units and all should work fine."

I am with you on that. I already have the replacement part numbers from Snyder's if all else fails. Before pulling the plug on the present electronics, however, I just wanted to hear from readers if they have had a similar experience with LED taillights and if so, what was the cause and solution. With all the faith in electronic testing equipment tossed around here to solve the simplest ignition problems, I thought for sure there would be a way to test the exposed diodes on the taillight circuit boards. But as I say: I am no electronics wizard.
Marshall
 
I took an electronics class MANY moons ago and knew how then. While Ive used the basic knowledge since for other electrical pieces I have definitely forgotten how to do that part. Sorry I couldn't be much help on that.
 
You can check diodes for continuity/resistance. You should have continuity/close to zero ohms in one direction and infinite ohms the other direction.

That said, have you tried wiring the bulbs directly to your battery? Hold the socket part of the bulb against the frame/ground terminal and, using a length of wire coming from the non-grounded side of your battery, tap the little contacts on the bulb. That seems easier than trying to beep continuity on surface mount LED components.
 
Thanks for the additional suggestions. I don't know why I didn't think of it before to simply try a light bulb in the brake light portion of the taillight. I did that this morning. The bulb turned on when the brake pedal was depressed. So, electricity is reaching the socket, which is good. It's the upper portion of the LED circuit board for the brake lights that is definitely bad, while the lower portion for the red taillights works. We'll order just the new circuit boards from Snyder's and hope that solves the problem.
I'll post next week if the new circuit boards did the trick.
Marshall
 
For some unknown reason, tried 2 electronic flashers on 12 volt system and they didn't function properly. Went back to conventional 50 year old USA flasher and all worked. Rear LED's, front incandescent bulbs, no resistors added..
 
You nailed the problem right there: "50 year-old USA flasher". That speaks volumes about how quality in this country was once excellent and highly respected vis-a-vis off-shore junk. Ya' gotta' go back a half century to find it again, though! :(
M.
 
duke36 said:
For some unknown reason, tried 2 electronic flashers on 12 volt system and they didn't function properly. Went back to conventional 50 year old USA flasher and all worked. Rear LED's, front incandescent bulbs, no resistors added..
Click to expand...

Marshall V. Daut said:
You nailed the problem right there: "50 year-old USA flasher". That speaks volumes about how quality in this country was once excellent and highly respected vis-a-vis off-shore junk. Ya' gotta' go back a half century to find it again, though! :(
M.
Click to expand...

It didn't even occur to me that it was the flasher. I have the same setup as duke36, Thermal flasher, 1156A incandescent front, LED rear. 12v system, no resistors. I added a 'hidden' 3mm LED indicator light to remind me to turn them off...

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The upper brake light part of one of mine failed as well after about 1 year of use. I confirmed it wasn't a wiring problem so just bought a replacement lens. It has been working fine ever since. Mine is a 12 volt system. It happens sometimes with electronics.
 
Brake lights were generally always a higher CP rated bulb back in the incandescent era. Early cars just used separate bulbs between running and brake lights but eventually went to a two pole double filament bulb with the high CP filament being for brake light function. Turn signals were originally set up to "share" the brake light circuit so that the signal light could be seen well in daylight hours. This sharing made the turn signal switch rather complicated in order to isolate the brake light from the turn signal light during that function but still allow the brake light to work on the opposite side. Using LEDs can complicate this further depending on how everything is hard wired and how the turn signal switch is set up. Add a resistor in to that and it get's even more complicated.

LEDs generally only complicate things in the turn signal circuit due to current being the thing that makes the signal stat function as an on/off switch to blink the turn lights. LEDs don't draw enough current to make the old signal stat bi-metallic breaker work, sans the necessity for resistors to draw the needed current. A person might as well just use incandescent bulbs for that. Resistors defeat the purpose of the LED.

I would recommend that folks use all four turn signals assemblies as dedicated for turn only with no brake light or park light involvement, The signal lights that fit between the bumper bars would be a good choice since they are out of the way for the most part. Use of an electronic signal stat breaker would also be a good idea as long as it proves to be fairly reliable. It should if using dedicated lights.

LEDs, being diodes, are one way directional electronic devices. They pass current one way but not the other. This makes them polarity sensitive in a DC circuit. Observe polarity when testing them with a battery and remember that most old cars in the 6-volt era are positive ground. This makes the ground even more important.
 
I use amber incandescent bulbs in front, LEDs (Much brighter) in the rear, No resisters, Thermal flasher (bi-metal). No issue.

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