LED flasher relay for '76 Carrera 3.0

[91166 Carrera]

I have a '76 Euro Carrera 3.0 Targa. I want to install LED replacement bulbs in place of the original Osram #2721 incandescent in the dash gauges. I'm using a Uroparts flasher (4-pin). I'm not sure what the problem is but the turn signal bulbs both flash, one bright and the other dimly, depending on whether the switch is in the left or right setting. Also, the brake light flashes with the turn signal lights when the hand brake is pulled up. Is this a bad flasher or do I need a LED flasher? If I need a LED flasher (a 4-pin) which flasher do I purchase?

Another problem I have is with the generator light. When I replaced the original Osram #3898 bulb with a LED replacement the generator light stays on after the car has started. Typically the generator light turns off after the car is started, such as with the original Osram bulb. Could the socket be bad? It is hard to get the LED bulb in and out of the socket. Anybody with information on this?

Harry

[911obgyn]

I think you have to retain the incandescent bulb for the alternator unless you want to get into the weeds about which resistor you need to add to the circuit to correctly energize the regulator.

[Showdown]

These cars don’t work out of the box with LEDs, you have to make some modifications.

Buy:

https://www.spokeworksled.com/product-page/ep26-led-compatible-flasher-for-911-71-73-914

Or diy:

https://www.spokeworksled.com/ep26-mod-dual-indicator

[91166 Carrera]

911obgyn and Showdown, thank you for the information. Showdown, special thanks for the link for that LED flasher. I'm buying it today. Its so nice to have knowledgeable people in the Forum.

Best,
Harry

[spoke]

Harry, it was good to talk to you tonight. The EP26 LED-compatible flasher with K/C2 pin connected to ground should solve your flasher issues.

Below is the turnsignal arrangement on the 914 which is almost identical to your '76 911's turnsignal arrangement. Notice how the Right indicator is connected to the left turnsignal bulbs and Left indicator to the right turnsignal bulbs. This is not a typo. When the turnsignals are engaged, the flasher will power the K/C2 pin to 12V via a secondary relay in the OEM flasher. If your replacement flasher is flashing the indicators when you engage the ebrake, then the K/C2 pin is not functioning correctly.

In the EP26, I connect K/C2 to ground. Thus the right indicator will flash with the left turnsignal and the left indicator with the right turnsignal. You'll have to pop out the tach and pull the entire indicator socket for both indicators and swap them in the holes to remedy this oppositeness.

[91166 Carrera]

Spoke, your relay did the trick. So happy I was introduced to you. Shout out- if you have a '76 911, or something close, and want to upgrade your gauge lighting to LED then contact Spoke. Five stars. You're now on my Christmas list!

Harry
'76 Euro Carrera 3.0 Targa

[Walt Fricke]

If I understand the older style flasher relays, when you power it on a relay contact is in the on position for one thing or the other which is supposed to flash. So a resistance bulb comes on. The heat of this current warms a bimetallic or other spring, which then opens the circuit, so the bulbs go off. This cools the spring, which then closes. The closing produces the click of the turn signal. And repeat. Since the bulbs are part of the resistance which determines how much current is needed, stands to reason that they must have the right resistance.

Something like this. Newer systems undoubtedly are fancier and solid state, though I don't know how they generate the click.

[spuggy]

Originally Posted by 91166 Carrera

I have a '76 Euro Carrera 3.0 Targa. I want to install LED replacement bulbs in place of the original Osram #2721 incandescent in the dash gauges. I'm using a Uroparts flasher (4-pin). I'm not sure what the problem is but the turn signal bulbs both flash, one bright and the other dimly, depending on whether the switch is in the left or right setting. Also, the brake light flashes with the turn signal lights when the hand brake is pulled up. Is this a bad flasher or do I need a LED flasher? If I need a LED flasher (a 4-pin) which flasher do I purchase?

You can apparently convert (easily reversible) the early 4-pin flasher relay to a 3-pin EP36 relay (as per the 85-up cars) by adding a ground wire to pin 4 in the relay socket. Which lets you run LEDs in the repeater bulbs without the issues you describe. The 3-pin relays are also more easily available and considerably cheaper...

See targa80's excellent post here: https://forums.pelicanparts.com/porsche-911-technical-forum/819548-flasher-hazard-mods-my-80sc.html

Originally Posted by 91166 Carrera

Another problem I have is with the generator light. When I replaced the original Osram #3898 bulb with a LED replacement the generator light stays on after the car has started. Typically the generator light turns off after the car is started, such as with the original Osram bulb. Could the socket be bad? It is hard to get the LED bulb in and out of the socket. Anybody with information on this?

Not only are there potential issues with matching resistance necessary for the exciter coils if you change to a later alternator type/voltage regulator that needs more current (apparently later cars used 4w bulbs, which won't fit in the bulb holders/instruments in the earlier cars, thus the retro-fit resistor in the factory bulletin), I believe that there's also an issue as to which direction the current flow is going.

Makes no difference to the the bulb, which provides the same resistance in either direction and will light up for either, given sufficient current.

An LED by comparison, has very little resistance (device itself has very little, and the resistor built into the bulb package is only there to drop the supply voltage down to the LEDs working voltage- usually 1.2V to 3.6V, depending on color) in one direction - and basically infinite resistance the other way.

It acts as a one-way valve, or diode - the 'D' in LED - and won't light up or allow current to pass at all in the other direction. It will also potentially activate with relatively tiny amounts of forward current, that simply would not be visible with an incandescent bulb (filament wouldn't get hot enough).

You could, in theory, use a bi-colored LED (2 LEDs back-to-back in the same device, that show a different color depending on which way current is flowing). However, I've never seen any in an automotive package with a series resistor for a 12V supply, and would not expect to. You'd need to build this yourself (eg source bare bulb bases and the devices etc) - and would still need to add an external resistor appropriately selected to drive the coils hard enough without any bulb resistance in-circuit that they actually functioned as intended.

So, yeh, just put the bulb back in...