LED electrical puzzle

[Tom Wells]

I'm aware this subject has been beat nearly to death.

I have a new wrinkle on it that is still a puzzle for me. Here's a quote from my message on the firstcoastcobraclub.com web site:

I have encountered an interesting electrical puzzle. I have arrived at a compromise, but am still curious about why it happens and whether there's anything practical I can do to eliminate it.

The Cobra has six lights for brakes and parking. Two parking lights in the front, and four separate taillights.

All six bulbs are 1157 dual contact/dual filament bulbs.

I'd like to change all the bulbs to LEDs.

So far, if I put LEDs in the four taillights, everything works as it used to: all the stop/turn/parking lights work normally. It works fine with the original flasher.

If I put LEDs in the parking lights, everything works except the turn signals. The turn signals just never flash.

I have read that the old-style flasher just makes them flash rapidly, but that doesn't happen. There is no flashing at all.

So I got a flasher supposedly made just for LEDs and tried it - same result - no flashing at all.

I have reverted to the incandescent (two) front and LED (four) rear bulbs and the original flasher, and all works fine.

Question: is there a way to get the parking lamps converted without too much fuss, or should I just leave well enough alone?

Tom

[MOTORHEAD]

Hi Tom,
I would think that it might have something to do with the 4 tailite situation. LEDs draw very little current, so in a normal 2 tail lite circuit you have to add a load resister to make the flasher draw enough current to heat the flashers bi-metalic contact strip. Maybe adding the resistors to the front lites might solve the puzzle.
If not, just go with what works!

Ted

[Jim Vander Wal]

I had 6 bulbs in my Superformance. Switched all 4 rears to dual element LEDs. Everything worked as expected, flashed normally. When I changed the fronts to dual element LEDs, same type as rears, it wouldn't flash for turn signals. I tried the LED specific flasher units, still failed. It was easier to keep the incandescent 1157 bulbs in the front than to chase the demons. Jim

[Tom Wells]

Ted,

I tried the LED-specific flasher which is (supposed to be!) specifically made for the low current LEDs. No change to the symptom with all LEDs in place, i.e., no flashing at all.

Jim,

That's exactly where I am now. It's working (LEDs rear, incandescent front) but I can't stop trying to puzzle out why

Tom

[MOTORHEAD]

Tom; If two lites per side work in the tail lites, try two per side in the front. As a test, you only need to try it on one side. Take both leds for the front, put one in the socket and "clip lead" the other one in parallel with with the first. If that doesnt work, use the incandecent bulb parallel with the LED and see what happens.
Think: WWED (What Would Edison Do ? )

Ted
ps; Your car doesn't have the big brake lite/tail lite relay, does it ?

[Tom Wells]

Ted,

Thanks for the suggestions.

For now, I think Edison needs to get his front bumper, windshield etc etc back on so the car can be driven. It was just painted (don't ask) and I'm still reassembling it.

When I get some spare time I'll see about more detective work - I was just hoping someone else stepped in this particular one and could propose a quick solution. I'll take Jim's approach (let sleeping LEDs lie) for the moment.

And, no, I don't know whether I have that relay or not. The car is approaching its 18th (or is it 19th) birthday and was "custom wired" when built. Alas I didn't get a schematic. I do have the original Everett Morrison schematics but not sure any of that would apply to this car.

I seems to run fine so I'll start enjoying it again!

Tom

[krausewich]

Hi Tom,
I do not have Cobra specific experience, but I have read several things online that when upgrading bulbs to LED's on production trucks, you will require an inline resistor when it comes to flashers. This info was from the ramforumz.com website, but I imagine the electrical theory is similar. I know that when I upgraded my Ram's taillights to LED, there was a resistor box as part of the assy. for the brake light portion.

Good luck,
Mike.

[Blue66]

Great info..

[Unique427]

Switching from halogen to LED turn signals can introduce either a hyper-flash
or no flash/steady on condition with turn signals. The electro-mechanical
relays use load resistance from the halogens to switch on and off. LEDs
require only a fraction of power and hence produce very little load resistance.
You have (2) options here. Splice in a load resistor into each turn signal circuit
that mimics the halogen and fools the relay, or replace it with LED
compatible solid state relays. Option 2 is better and cheaper. Plus those
load resistors can get hot enough to melt plastic. You will need to replace
(2) relays. One for turn signals, the other for hazard lights. My relays
were (2) prong Tridon 552. Some of you may have (3) prong relays.
Superbrightleds.com offers a (3) prong LED compatible relay.
1) CEC Industries LED Compatible (2) Prong Relay # EF32SS-R ($18.39 / Amazon)

SPECIAL NOTE:
After switching to LED compatible relays, if you still experience a
no flash/steady on condition, the relay socket was reverse wired. Old
electro-mechanical relays are not polarity sensitive and hence the
technician who wired it did not care to check. No worries. Easily
corrected with a relay polarity adapter. The CEC Industries EF32SS-R
plugs into the adapter and together they plug into the relay socket.
(1) or both relays could be reverse wired so test individually.
This should solve any persisting issue after installing LED compatible relays.
1) United Pacific Relay Polarity Adapter # 90650A ($1.99 / Summit Racing)

ADDITIONAL NOTES:
If you leave only the front turn signal lights as halogen and convert the rear
brake and turn signal lights to LED, there's likely enough load resistance
in the circuit to trip the mechanical relays without changing them.

Also, best results are had by using LED's color matched to the lens.
Use amber LEDs for amber lens and red LED's for red lens.
White works for everything but the brightest most vibrant light
transmissions comes from color matching.

1) iBrightstar 1157 BAY15D LED – Amber #X001JCP9KP ($16.99 pair / Amazon)
2) IBrightstar 1157 BAY15D LED – Red #X001IPJ4EF ($16.99 pair / Amazon)

License Plate Lights:
This is for Lucas L467 License Plate Assembly and requires (2) LED bulbs.
1) Superbrightleds BA9S LED 5 SMD Tower 6100K # BA9S-CWHP5 ($3.95 / Superbrightleds.com )

[Tom Wells]

Unique,

Thanks!

One part of the puzzle is definitely solved.

And as always, one solution leads directly to the next puzzle.

The solution to the first part of the problem is that the original flasher was indeed wired with reversed polarity. I corrected the polarity and the incandescent-style original flasher continued to work as before: LED taillights and incandescent parking lights, all 1157 bulbs or equivalent.

So I breathlessly substituted the solid state flasher and lo and behold it flashed! Well, at least the dashboard lamp flashed. Alas, the external lights did not flash at all. Not any of them.

My suspicion is that there may be a secondary relay somewhere that causes the rest of the problem. I have no idea whether or where that one may be, so the setup will go back to the incandescent-style flasher and parking lamps, and LED taillights.

I have no accurate wiring diagram, so chasing the next part of this problem will be at least as interesting as before.

At some indeterminate future time I plan to revisit the problem and maybe make another step, but not today!

[Unique427]

Tom,
There is a 2nd relay if you have a switch for hazard flashers.
2nd relay must also be changed out and polarity tested.
Will cause no flash issues if not changed out.
2nd relay likely mounted conspicuously on/near the fuse block.
If that's not the culprit then I'm not sure what it is.

Put your hazard flashers on and listen for where the telltale 'tick-tock' sound
the original relay makes when it's flashing your lights on/off.
That sound will lead you to the relay location.

As a final note, when you complete the change over to all LEDs, those
new solid-state LED compatible relays will likely lack the 'tick-tock' sound.
You'll have only dashboard light cues for turn signal and hazard flashers.
With Cobra side-pipes you can't hear it anyway so no loss. HA!

[Tom Wells]

Unique,

Here's the next chapter in the continuing stooory of the LEDs and flashers...

I put brand "A" LEDs in the front. No joy with either flasher - nothing happened. No lights, no flashing, no dash light.

Brand "B" gave parking lights or flashers with the LED flasher. If the parking lights are on, no flashing. If the parking lights were off, they flashed fine.

Both brands (A&B) are ??? from China I presume, but obviously have differing electrical characteristics, probably with respect to grounding.

I noticed that if I left the flasher on, putting the incandescent bulb partly into the socket gave a tic-toc at the flasher but no illumination, saying to me there's probably a difference in the way all three sets of bulbs are internally grounded. This didn't happen with the LEDs.

BTW, the car has no 4-way flasher capability as far as I could see. No button and no (obvious) 2nd flasher.

Fascinating...