How To: CptTripps' Cat-Eye LED Light mod Options

[Spoke]

I've noticed that the blinker in my 71 blinks the same rate regardless if the rear turn signal bulb is in or out. The front still has a bulb.

[mrbubblehead]

Thought I read somewhere the whole turn signal blinky circuit was dependent on sensing the resistance in the bulbs??? No??

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I thought so too. Maybe not? (IMG:style_emoticons/default/confused24.gif)

I was under the impression that a certain amount of current draw was needed for it to work correctly ...
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it does rely on the load from the incandescent lamp. but you can wire a load resister in parallel with the LEDs to get the relay to blink. the resisters are designed for this purpose. i think they also make a flasher relay specifically for LEDs so you woudnt need the load resistors at all.

nice write up. im in.

[bulitt]

So, possibly a resistor will be needed in the circuit.
Found this write up on the club site.

There are three parts of the flasher. The primary relay (I'll call it) switches on and off and provides an on/off voltage to ANYTHING connected to it. This is controlled by the second part, a solid state timing circuit. When a load is detected, the timing circuit starts pumping out a little square wave to the coil of the primary relay, causing it to turn on and off.... By doing it this way, the frequency of the on-and-off is independent of the load, because the load on the timing circuit (ie, the relay coil) is always the same.

Now it gets interesting. Notice that the output of the primary relay actually passes in series THROUGH the coil of the secondary relay. This coil is a special kind of coil that is normally used in magnetic circuit breakers rather than relays. It is a CURRENT COIL, and the secondary relay will close only when enough CURRENT is passing through it. Relays generally have voltage coils that close when the correct minimum voltage is applied. The current coil is designed to minimize voltage drop, so it is only a few turns of relatively heavy gauge wire.

After it has passed through the coil of the secondary relay, it exits the flasher to be used for anything in the car that needs to flash- directional signals, hazard warning, emergency brake light, or (at least in my car) the fasten seatbelt light.

The secondary relay will create a second flashing output, but only if enough current is passing through the primary flashing relay. The threshold current that trips the secondary coil will cause a secondary flashing output when the turn signals or the hazard flashers are engaged, but not when the emergency brake light or the fasten seatbelt light is engaged. They still flash because they are attached to the primary relay, which is oblivious to load, but their load isn't enough to cause the secondary output to flash.

Why bother? Well, the law required a cockpit-visible indication of a burned out direction signal bulb. So if you turn on your left signal and the front bulb, say, is burned out, the rear signal will still flash, but there will be no secondary flashing output. And, you guessed it, the secondary flashing output goes to the indicator light on the dash.

You can actually hear it if you sit in your car with the engine off, but turn the ignition on. Pull up on the emergency brake and listen, and then turn on one of the direction signals. The click gets audibly louder because both relays are clicking instead of just the one.

I drew the '73.5-'76 circuit first, because it's easier to figure out. This secondary flashing output goes directly to the only turn signal indicator in the tach (via the blue/white wire). The other side of that indicator is grounded.....

So, the driver-visible indication of a burned out bulb is- when the turn signal indicator works fine for one direction, but remains dark when you switch to signal for the other direction.... There is a bulb burned out on the latter side. Or something else that can reduce the current flow below what is required to trip the secondary relay... Like corroded contacts, corroded socket, wrong type bulb (not bright enough), bulbs replaced with LEDs, whatever that reduced the current below the flashing threshold.

[TargaToy]

Thought I read somewhere the whole turn signal blinky circuit was dependent on sensing the resistance in the bulbs??? No??
Hope it works!

I think that's true but when the motorcycle guys switch from standard bulbs to LED, they just run the appropriate resistors in-line so that they retain their "blinky". I'm sure that could be easily done with this setup.

[bulitt]

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Didn't want the Cpt ditching his efforts if the turn signal doesn't work.

[CptTripps]

I was thinking about setting up a flasher relay and the front/rear LED light packs that I have...just to see what resistor we need.

I'd really like to figure all of this out.

[Spoke]

I was thinking about setting up a flasher relay and the front/rear LED light packs that I have...just to see what resistor we need.

I'd really like to figure all of this out.

Interesting that I removed both front and rear turn signal bulbs and my flasher flashed at the same rate as with bulbs.

Has anyone else tried this little experiment with their 914?

[bulitt]

Guess the board electricians will weigh in. Thinking you put an ohm meter on the turn signal bulb and discover what resistance it is?

[mikesmith]

You just replace the flasher with one designed for LEDs. That part is easy.

[CptTripps]

I ordered a couple different "LED friendly" flasher relays. I'll have them at some point this week so I'll set it up on the bench and see.

If anyone in the Cleveland area has a 914 they want to swap the bucket out on to test, I'm happy to lend it to them. I'd put it in my car, but I have no wiring harness in there right now.

[Mike Bellis]

Some of the 914 relays will work with LED's and some won't. I'm not sure what the difference is. It may come down to where the relay gets it's reference current; Through the indicator lamps or through the dash lamp.

I fried my relay with all LED's (except the dash). Now I run LED rear and incandescent in front. No problems.

Early flashers use a bi-metallic strip that bends with heat (current). This type will need resistors to drop voltage and increase current. Modern relays have a timer circuit that is less load dependent.

914's use a separate circuit for the dash indicator. This is why there are 2 relays inside the flasher. A modern, non 914 flasher is difficult to make work with the German wiring system and turn signal switch.

Bottom line... If it works with LED's, keep it. If not buy another flasher until you get one that works.

[914forme]

Doug is also using a completely different harness with new flashers relays. I'm thinking he's not going to be limited by the 914s 1960s wringing harness technologies. Unless his plans have changed, if they have you just add a load back into the circuit. Well Documented in the hot rod circles.

Or just use these (IMG:style_emoticons/default/dry.gif) Load for LED Turn Signals

[3d914]

Doug, nice job - I like it!

You gonna provide part numbers or will you be making these up for others to purchase?

[CptTripps]

Stephen is correct. I have a completely custom wiring harness. But I'll still need a proper relay for them to work.

Using a load resistor would be pretty easy. I'll have to measure the bulb against this light pack to see what the diff is.

[AfricanHijinx]

very nice

[AndyB]

I was thinking about setting up a flasher relay and the front/rear LED light packs that I have...just to see what resistor we need.

I'd really like to figure all of this out.

I installed the tower design bulbs from supebrightleds.com. I have not put my resistors on the front but they still blink just like the rear. The only difference is my turn indicator light wont come on. Not a show stopper to me.

[mrbubblehead]

I was thinking about setting up a flasher relay and the front/rear LED light packs that I have...just to see what resistor we need.

I'd really like to figure all of this out.

that is the indicator telling you you have a lamp burned out. the flasher relay is working like it should.


I installed the tower design bulbs from supebrightleds.com. I have not put my resistors on the front but they still blink just like the rear. The only difference is my turn indicator light wont come on. Not a show stopper to me.

[effutuo101]

Some of the LED pre fab lights have built in resistance on the boards that house the LED's.

[mikesmith]

Some of the LED pre fab lights have built in resistance on the boards that house the LED's.

This is a stupid idea. LEDs hate being hot. The resistor turns current into heat (quite a lot of it).

Get a LED-friendly flasher. They aren't hard to find. I want to say I'm using a Tridon EP26, but I'd have to pull the fuse panel out (again) to check.

[CptTripps]

Added 2 white spots behind the light tonight to see if that'd make for a decent DRL idea. You be the judge.