Patrick - LED Taillight problems

[patrickt]

Originally Posted by DanEC

I'm going to remove a tail light so I can examine the socket better and see if I can figure out what the incompatibiity is.

Excellent. You are well on your way now to earning your EE degree, from ClubCobra University, of course.

[DanEC]

Everything checks out. Bulbs light up in the light fixture using my battery charger. I reinstalled in my car and with my test light I show power at the connection but the bulb doesn't light. I checked polarity with a standard 1157 and they are the same. Only thought is that voltage off of battery is not sufficient to energize the LEDs on the tail light circuit - so next I'm going to wheel the car out and start it up and see if running voltage will light the tail light circuit.

If that doesn't work then I'll call superbightled since they haven't answered my email yet.

Edit - when I said polarity that was a misnomer. What I checked was orientation of the two illumination circuits and compared to a standard 1157 bulb.

[patrickt]

Originally Posted by DanEC

Only thought is that voltage off of battery is not sufficient to energize the LEDs on the tail light circuit - so next I'm going to wheel the car out and start it up and see if running voltage will light the tail light circuit.

Or you have quite bit of resistance "upstream" from the tail light fixtures. That resistance translates in to voltage drop. The easy way to test that is just run a ten foot piece of lamp cord from the positive side of your battery to one of the fixture's wires (first brake/signal then tail), and run the other leg of the lamp cord to the negative side of the battery and to the ground of your light fixture. If the LED lights up nicely doing it that way then you have voltage loss through that circuit when it's trying to operate normally. It could either be on the positive or ground side of the fixture. My feeling is if that battery has enough juice to start your car then it has a enough juice to light your LEDs.

[DanEC]

Talked to Superbrightleds and they were totally baffled. It sounded like they had never heard of a problem on the tail light circuit - only the signal and brake light one.

Did a little more testing and this is where it gets a little wierd, I have the driver-side light hooked up to the car but hanging loose. With light switch off, I connected the ground on my battery charger to the bulb socket. With both the yellow and red harness wires plugged in - I touch the + lead to the yellow terminal and the bulb lights - touch it to the red terminal and no light. I unplugged the yellow terminal and touched the + lead back to the red terminal and the bulb lit. Also touched it to the un-connected yellow terminal and that side lit also. It will not light on both circuits with the yellow lead plugged in.

Apparently there is some sort of issue backfeeding through the trailer relay unit is all I can figure. It looks like I've gone as far as I can and these just are not going to work in my car for some reason. May Bob will think of something.

My next project is to try to get my lake pump for the sprinkler system running by replacing the 220/24 starter relay. Hope this electrical project goes better.

[glenview289]

Some time back, about 3-4 years ago, I converted my Unique to LEDs. At that time there was discussion about the low current draw of LEDs that would notwork with some trailer relay switches. I'm sure a search on this will bring up something. Not an EE, but do remember this could be an issue.

Bill

[patrickt]

Originally Posted by glenview289

Some time back, about 3-4 years ago, I converted my Unique to LEDs. At that time there was discussion about the low current draw of LEDs that would notwork with some trailer relay switches. I'm sure a search on this will bring up something. Not an EE, but do remember this could be an issue.

Bill

To help Bliss with his tail light/trailer relay problems, I went out and measured the voltage drop across my trailer relay (with the circuit operating, of course). My stock trailer relay was eating up 1.7volts with the battery source putting out 12.5volts. There are better relays than our "stock" ones. They are touted as "heavy duty" trailer relays. He's had problems before with his relay, too. Some of the guys in other forums report voltage drops of well over 2 volts for some of the relays.

[YerDugliness]

Originally Posted by glenview289

Some time back, about 3-4 years ago, I converted my Unique to LEDs. At that time there was discussion about the low current draw of LEDs that would notwork with some trailer relay switches. I'm sure a search on this will bring up something. Not an EE, but do remember this could be an issue.

Bill

I remember that thread...didn't the end result be that a resistor had to be added at the back of the car for the lights to work?

It's been a while, but there's that dim memory, perhaps I'll go back to the Unique website and see if I can find the thread.

Cheers!

Doug

[Xack]

Originally Posted by DanEC

Everything checks out. Bulbs light up in the light fixture using my battery charger. I reinstalled in my car and with my test light I show power at the connection but the bulb doesn't light. I checked polarity with a standard 1157 and they are the same. Only thought is that voltage off of battery is not sufficient to energize the LEDs on the tail light circuit - so next I'm going to wheel the car out and start it up and see if running voltage will light the tail light circuit.

If that doesn't work then I'll call superbightled since they haven't answered my email yet.

Edit - when I said polarity that was a misnomer. What I checked was orientation of the two illumination circuits and compared to a standard 1157 bulb.

What is your steady-state battery voltage? If you do not have 12-13 volts at the bulb, there is a resistance probably at the switch or between there and the bulb(s). Disconnect the battery and Check resistance on the LOW resistance setting on your VOM. Measure resistance between the bulb ground on the connector to the battery negative terminal. Also measure resistance between the bulb power and the connector on the load side of the light switch. Any resistance here will drop your voltage to the bulb(s). You should not see more than 1 or 2 OHMS of resistance in your wiring. LED's are voltage sensitive, meaning they will not light up if the source voltage is too low. They sink relatively low current compared to incandescent type bulbs. Incandescent bulbs (current sensitive) will turn on if they can sink enough current to glow the filament, even if source power voltage is low like 9 volts or so.

You can also run a wire from the battery ground and attach it to your bulb ground to see if you have a grounding problem. (I suspect a poor ground circuit) If you don't see improvement, the problem is on the power side, meaning you have a poor connection on the switch or any connection between the switch and the bulb filament(s). Check voltage at the fuse, switch, and all connections all the way to the bulb to see if you are getting anything but the same voltage measured at your battery (terminal to terminal).

[DanEC]

The car is down for winter maintenance items right now but it runs 14.5V at idle. ERA runs grounds from each tailight frames to a big bolt for the bumper brackets and I install serrated washers at all grounds. All are tight and I have multiple grounds installed from the drivetrain to the frame. Everything functions properly and is bright (for filiment bulbs). If I had ground problems I think it would show up in the blinker and brake light circuit also, which worked fine with the LED bulbs.

I mean the LED bulbs are working fine in my GTX with a 47 year old wiring harness, taillights and Mopars known reputation for electrical issues. A large number of these things burned up by the mid-70s due to electrical problems. If it was simply a bad ground or resistance issue that was the problem I can't explain how they could possibly function in my old Plymouth.

I appreciate the pointers. When I get the car out again and it warms up I may get out my meters and do some more checks on the tailight circuit. But I kind of wore myself out earlier, trying to fix something that wasn't obviously broken. I'm curious to see how Large Arbor does with them.

[Xack]

.....

[Xack]

Originally Posted by DanEC

The car is down for winter maintenance items right now but it runs 14.5V at idle. ERA runs grounds from each tailight frames to a big bolt for the bumper brackets and I install serrated washers at all grounds. All are tight and I have multiple grounds installed from the drivetrain to the frame. Everything functions properly and is bright (for filiment bulbs). If I had ground problems I think it would show up in the blinker and brake light circuit also, which worked fine with the LED bulbs.

I mean the LED bulbs are working fine in my GTX with a 47 year old wiring harness, taillights and Mopars known reputation for electrical issues. A large number of these things burned up by the mid-70s due to electrical problems. If it was simply a bad ground or resistance issue that was the problem I can't explain how they could possibly function in my old Plymouth.

I appreciate the pointers. When I get the car out again and it warms up I may get out my meters and do some more checks on the tailight circuit. But I kind of wore myself out earlier, trying to fix something that wasn't obviously broken. I'm curious to see how Large Arbor does with them.

Ok. But you've only proved the bulbs work by putting them in another car. That's good, but your problem still exists on your Cobra. The bulbs are good. The circuit works as long as your battery charger provides higher voltage than is available by just your battery alone. New washers don't mean you've fixed a bad ground.
Good luck!