Patrick - LED Taillight problems

[patrickt]

Make sure you run the temporary ground wires to the front lights as well. There has to be a "spill over" between parking lights and turn signal lights and the front lights' ground could very well be the culprit.

[DanEC]

With a 12.64 battery voltage, parking lights on, key off:

Driver side tail light 12.24 volts

Pass side tail light 12.21 volts.

Interestingly I was picking up .2 volts at the turn signal lead at the lights.

How am I supposed to check voltage drop across the trailer relay? When flashing the voltage is jumping up and down of course. I thought I might get something from the red wire on the car side from the brake switch by pushing on the brake pedal but it was only a few volts. I also noticed the same .2 volts across the relay with the parking lights turned on.

[patrickt]

With the key on, and the brake pressed, put one lead of your VOM on the middle RED input wire and the other lead on one of the two output wires. The reading will be the voltage drop attributable to the trailer relay.

[DanEC]

Originally Posted by patrickt

With the key on, and the brake pressed, put one lead of your VOM on the middle RED input wire and the other lead on one of the two output wires. The reading will be the voltage drop attributable to the trailer relay.

Allright I will try that. I basically did that but since it was a low reading I didn't record it. In the meantime, using the brake lights I got these voltage figures

tail light to ground, brake lights - 10.5 volts

trailer fuse connection to ground, brake lights - 10.54 volts

[patrickt]

I pulled my notes from the last time I took all my stuff apart. I have a voltage drop across the trailer relay of 1.7 volts. The output of the trailer relay is 10.5 volts. You DO have temporary ground wires running to all four corner lights, correct?


EDIT - "trailer" relay, not "voltage" relay.

[DanEC]

Testing across the relay I got 11.95 volts at the red wire and 10.45 volts at the fuse holder. Not sure why it was .1V lower at the fuse holder this time?

Man - crawling under the driver side dash of a Cobra at 63 years age is pretty tough.

Edit - no, no temporary grouinds hooked up at this time. All of this has been with the factory grounds.

[patrickt]

Remove the two fast blow fuses adjacent to the trailer relay, leave them out, and hit your brakes, and turn on your turn signals. Do any rear lights at all come on? Do the front lights behave as expected?

[DanEC]

I'm through for tonight - will try that tomorrow.

Thanks

[glenview289]

Dan, listen to Patrick on this one. You have to eliminate for sure that the ground is good before anything else or you will or have been wasting your time. Bad grounds are the cause of intermittent problems 90% of the time. These cars are known for these type problems associated grounds.

Bill

[patrickt]

Alright, we'll continue "splitting apart" the circuit until we isolate the portion that is causing the misbehavior. For the next step, you will need a simple 12v test light, not a VOM. Assuming the car's lights act normally with the fuses pulled, we'll put a new bulb load on the trailer side of the removed fuses and see if they just come on normally or whether the misbehavior is present even without the rear lights wired but with just a 12v test bulb

[DanEC]

Tried two tests this morning with inconclusive results:

1. Switched the parking light leads and the flasher leads on both rear sockets with the leds in case they are oriented 180 deg opposite of 1157 bulbs.

Key on, turn signal on - everything operated correctly. Before switching - all 4 lights flashed including trunk lights.

Key on, parking light on, turn signal on - the fronts flash but the rears don't. All leds on the rear bulbs were illuminated. Before switching - all lights worked and operated correctly.

2. Pulled trailer relay fuses:

Key on, turn signals on - turn signals flashed only at front

Key on, parking lights on - all lights came on, only led units associated with parking lights were lit in rear.

Key on, parking lights on, flasher on - all lights came on, only leds units for parking light lit, only front lights flash - nothing flashing at rear.

Anything?

[patrickt]

Maybe. With the two fast blow fuses removed attach two 12v test lamps, not a VOM, to the trailer relay side of the removed fuses and to a nice ground. Then repeat the test. If everything is working normally, when the key is on and the turn signal is on, the front lights will flash and the appropriate 12v test lamp will flash there in the driver's seat. With the parking lights on, the back tail lights in the car will be lit, the front parking lights will be lit, and all will remain lit when the turn signal is turned on, but only the 12v test lamps will blink along with the front turn signal light, the rear turn signal lights will not blink.

Just to double check, you do have those four temporary ground wires running to the four corners of the car, right?

[DanEC]

Originally Posted by patrickt

Just to double check, you do have those four temporary ground wires running to the four corners of the car, right?

No - I don't have that many alligator clips. I can work on rigging something after lunch but I can see and feel each ground connection. They are not going to get any better. I can jumper the front and rear lights together and try to run them to the battery. But I don't see any of the testing that would suggest a ground issue - under certain situations everything works 100% properly (1157 or 2357 bulbs and rear LEDs as long as parking lights are on)? I don't have any intermittent operation, I don't have any dead circuits.

[DanEC]

OK - tied both sets of tail lights and front parking lights together with an auxillary ground wire and then ran wires from them to negative battery pole.

One of my test lamps was burned out so I only had one and had to substitute a VOM for the other. With the fuses out I turned the key on and then the turn signal. The test lamp flashed on the one and the VOM showed a current fluctuating with the flasher unit on the other.

I put the fuses back in and re-ran testing everything stock with the ground wires tied in. Everything still operates as described earlier - no change.

Realized I didn't test everything you said with the fuses out. Took the fuses back out - hooked up test light and VOM on fuse holder, turned on key, turned on parking lights, turned on turn signal. Front lights flashed. Test light and "VOM recorded power to tail lamp flashers. Also tried brake and got about 10.5 Volts when it was pushed. But nothing flashed at the rear.

[DanEC]

I just had a thought (no snide remarks please) - the people who have chimed in on this thread and said LEDs work in their tail lights in ERAs, have the round tail light option which I believe uses 4 bulbs instead of one being a reflector. Kevens2 has round lights, I know Patrick does, I think Large Arbor does. I have the rectangular tail lights with one bulb each.

Possibly, it takes the 4 LED lights together with the front ones to create the resistence properties necessary for everything to work. Without my parking lights on there just isn't enough load in the system and something is going wrong. When I turn on my parking lights the extra load on the system brings everything on and it works fine.

Is there anyone out there who hasn't given up on this thread already, with rectangular lights and had sucess with LEDs in the tail lights.

[patrickt]

I have the rectangular lights. Put everything back together, with the LEDs in the back, and REMOVE the #6 fuse. Try turning on your tail/parking lights. You shouldn't be able to because the fuse is out. Now, try your turn signals and see if they work normally.

[patrickt]

Now, assuming, with Fuse #6 out of the car, and both of the two little fast blow fuses installed properly, the LED turn signal still flashes all four corners regardless of whether you're signalling left or right, then I want you to remove ONE of the fast blow fuses and try the turn signals, in both directions, and report the results.

[DanEC]

Duhh - yeah guess I should see you have rectangular in your avatar. But, I think you have wired in a third brake light too - which may add some load somehow.

I'll see what happens with #6.

[patrickt]

You might not have noticed this, but see if when all four corners are flashing, because you're just signalling left or right, and Fuse #6 is out of the car, look and see if the panel lights for your gauges are also blinking ever so slightly. That would be a real clue if that was occurring.

[DanEC]

I pulled #6 fuse killing the parking lights. When I turned the turn signals on all 4 corners and license plate light flashed including the parking light led units in the tail lights. Turn the parking light switch on for the heck of it and there isn't any change.

Reinstalled #6 fuse and pulled one fast blow TR fuse. Key on and turn signal on - all 4 corners flash with the one TS direction. In the other direction only the front light flashes and the rear are all dark. License plate light also flashes so turn signal circuit is energized.

Pulled #6 fuse and one TR fast blow fuse, key on, parking lights off, turn signal on - all four corners flash including the parking light led units as well as the flasher ones. Flipped parking light switch on but no different.

Forgot to check with #6 fuse out but I tuned off the parking lights and turned on the turn signals and the panel lights do blink with the lights. I hadn't noticed before as I had the adjustment turned to off.

Grounds still hooked up from lights to battery.