Patrick - LED Taillight problems

[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

[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.